Maybe I’m taking crazy pills, but I’m still stuck on “why the hell does a TUI need to run in terminal React by way of JavaScript”
The fact that Anthropic felt the need to buy a runtime so they could make their TUI better speaks more to the quality of engineering than anything else IMO.
If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.
It largely works and it's a massive business success. This is the classic engineer asking the 'why this technology?' to what amounts to a business question.
They chose it early on, it works, and it makes obscene amounts of revenue. End of story. That doesn't mean it was the "greatest" choice, or has a perfect technical architecture.
Rewrites are never easy, even the bun rewrite. But a non-UI developer tool with a rigid API surface contract (and associated tests) will always be easier to trust after a rewrite than a partially tested UI tool with ambiguous functionality.
>It largely works and it's a massive business success. This is the classic engineer asking the 'why this technology?' to what amounts to a business question.
Your counter argument would be valid for a 2000 or a 2020 business decision about some tech stack.
But the whole point of their product is that it supposedly nullifies such "business" concerns around the use of technology, by making it cheap and fast to build whatever you like automatically.
That they wont, or worse, couldn't, speaks against that.
> But the whole point of their product is that it supposedly nullifies such "business" concerns around the use of technology, by making it cheap and fast to build whatever you like automatically.
This is a spectrum, it's not just 0% vs 100%. Even Fable frakked up a few things really badly in my professional work (though to its credit after a very detailed 2h chat it self-corrected and fixed all the blunders).
I would also challenge "fast" -- Fable (and I assume Mythos) are wicked fast and efficient and even they can't compensate for f.ex. slow recompilations or test suite reruns or security scans, linters etc.
Reminder that the Bun's Zig-to-Rust rewrite took 11 days with dozens of agents working 24/7 and the author put the cost they'd pay (if they had to pay) at about $168k.
Billions of dollars of annual revenue go through Claude Code, and the people who work on it must be a lot of millions in headcount.
The time matters a fair bit, it's probably time someone can't spend breaking things in the name of new features, but if rewriting the stack had even a tiny impact on retention or driving higher usage, it would pay back that $168k.
>Reminder that the Bun's Zig-to-Rust rewrite took 11 days with dozens of agents working 24/7 and the author put the cost they'd pay (if they had to pay) at about $168k.
For an entity like Anthropic that's not even the cost of a single developer for a year. It's closer to what they pay a chef on premises.
That the showstopper for a better Claude agent is that they'd need to pay $168k or event $1M or even $10M in costs, can't be used as an excuse.
Lets see what happens in the future. From my experience cost of maintaining this amount of shitty code explodes pretty quickly. We will see in a few years if SW development in all phases using agents is that much automated and easy as people now predict.
> Reminder that the Bun's Zig-to-Rust rewrite took 11 days with dozens of agents working 24/7 and the author put the cost they'd pay (if they had to pay) at about $168k.
Does anybody really believe that it only took 11 days, one engineer and $168k in tokens?
>2. Rewrites and/or writing something in a native app or program is harder and more time consuming
Why would it be harder and/or more time consuming rather than the opposite? It's like having full specs and a full test-suite to match against the result you want.
> I just don’t see how one can say that building things reliably good is easy now when the company providing these tools can’t even do it well.
I don't know how you can't see it, to me it's blindingly obvious: risk aversion.
Let's say the risk for a problem is 1%; hell, let's put it at 0.1% even. For a company at this scale even that amount of risk is too much.
I trust Opus/Fable to drive prod database migrations and backfills. I don't trust it with our financial ledger. I trust it with part of the infra. I don't trust it with backups. Etc.
You and others are arguing against a premise that nobody defended, namely "Claude can rewrite everything, for free and with zero mistakes". A bit of a straw man, don't you think?
And that's not even touching the fact that writing a GUI app is difficult for LLMs due to difficulties in it getting feedback and a "feel" whether it delivered what was asked (though I know people are working on it).
> I think I am willing to take it as an axiom that a native version of CC would be superior from a user perspective. Performance, etc.
How does that follow, and from where? I never once noticed any visual jank/lag in the TUI; not in iTerm2, not in Kitty, not in Alacritty, not in WezTerm and not in Ghostty. And even if we exclude those two, me and many other devs are quite fine with a TUI and don't miss a GUI program for everyday coding.
Not saying that our preference is superior -- but it'd be strange to blatantly claim: "for dev purposes, GUI > TUI/CLI".
> by making it cheap and fast to build whatever you like automatically.
Cheaper, but not free (if you don't buy into the marketing promises too much). The bigger the project, the bigger the cost, even with a discount.
At the same time, the early versions weren't very good and you can be sure that any rewrite will also need to be similarly iterated upon until it is also good enough and polished.
If you do that and don't spend enough effort on making it be something polished --> your competitors have a better product and you lose.
If you pause feature development to give enough effort to the initiative, you don't get to add new features quickly enough --> your competitors have a better product and you lose.
Maybe their priorities lay elsewhere, like how I've noticed that the desktop app version of Claude Code has gotten both faster (no 2-4 second lag when switching conversations), more stable and usable over time, to where I enjoy using the models because of it, not in spite of it (though not that they haven't had bumps along the way, like that one cache invalidation issue, or how people didn't like the auto accept timeout thing). I don't doubt that you can get pretty far with gradual patches and improvements, instead of only big rewrites.
Honestly it's really cool for me to see Kimi having their own CLI too, same with OpenCode, Pi, Hermes (well more of an agent than just a coding harness but you get the idea) - there's so many competing solutions out there, each good or bad in unique ways.
Just wish we'd see similarly many GUI solutions, for now OpenCode GUI seems like the one I've settled on (cross platform and supports most models), though it's not exactly ideal either (feels a bit barebones, especially in regards to sub-tasks and progress/plan tracking, even ZCode seems a bit better in that regard, it was actually surprisingly good after they pushed out some updates).
I don't think they bought them just for the claude-code gui harness as it is now. it's to have strategic control over some software runtime they can use to do other things related to verification, deployment, and end to end value delivery. Same reason other companies are buying up dev tools.
By the same argument, why does it matter from the technology stack side? It doesn't just nullify the business concerns - it largely nullifies the tech stack concerns. Your preference doesn't matter if you aren't touching the code and the product works for your user base.
> But the whole point of their product is that it supposedly nullifies such "business" concerns around the use of technology, by making it cheap and fast to build whatever you like automatically.
Eventually? I am sure they would agree. Currently it's you (and lots of people like you) who are doing the supposing, not Anthropic.
I have been working all day every day in Claude. I loathe their bug-ridden UI. Every release is a new crop of bugs, sometimes the old ones get fixed, usually not.
Any kind of scrolling back, copying text, using their menu system - basically anything that isn’t typing characters has had/still has unaddressed bugs.
OpenAI shipped a competitive model and I’m over in Codex now. I have yet to hit a bug.
If you’re holding the SOTA crown, people will put up with your buggy mess. As soon as that crown slips your pile of trash becomes a huge liability.
They succeeded in spite of their tech choices. Their model outshone it, which is an extremely rare thing to happen and not something they could've counted on. In any other timeline they could've/would've been hurt by their choices.
It's like "why did you go all in on buying scamcoin 3.0 as your investment strategy?" -- "I 5xed my money! End of story! It was fine!"
As much as an enthusiast dev like myself hates it -- this is innately true, way too often.
I am 46 y/o and still excited to code and solve problems with code and I still have trouble to admit to myself sometimes that people make dozens of millions with PHP and the tech hardly matters when you can throw bodies at the problem (and when that throwing of bodies at the problem actually solves it, of course).
> I still have trouble to admit to myself sometimes that people make dozens of millions with PHP
Or many billions. eg. Facebook was originally written in PHP.
As a 52 y/o who cares deeply about software development as an art I don't have trouble admitting that the tech hardly matters relative to the economics, that was obvious to me very early in my career.
I have just never really cared because there has always been a path where you can have a decent career being paid to work on and with good technology in spite of the fact that the technology wasn't important to the economics.
I do fear that the rapid adoption of LLMs will probably cause the path I took to narrow considerably. There will likely be less companies willing to pay people to work on elegant technology when they are all competing against endless code generation machines (and this is assuming software companies can exist at all in this future). But at my age that's more of a concern for younger people than me.
Apply this reasoning to any other industry. Yes the average person is not the judge of the quality of a doctor or engineer. That doesn’t invalidate it. You want a doctor who cares about medicine , not whatever will accomplish a business goal.
Eh, the rendering of Claude Code is genuinely such a mess. I have quit claude code over it because when used as a terminal in PHPStorm it sometimes gets so bad that it becomes hard to use.
This isn't a minor nitpick, it's a pretty major UX issue.
Not saying it's like a massive business downside because I'm just one of a few users, maybe this affects their bottom line a little bit, but probably not by much.
Regardless, switching to pi has been a nice breath of fresh air. It just renders well and smoothly and handles terminal resizes well, which is especially important when used in a terminal window in PHPStorm.
Truthfully, the terminal in Jetbrains IDEs just isn't that great. It's gotten a lot better with their rewrites (yes, plural) of the last years, especially on Windows, but it can still be pretty dodgy.
It is rarely the case that technology choice is the make-or-break when it comes to whether a product is successful and achieves widespread adoption. Some choices are less ideal than others, but at the end of the day if you manage to make something that people want, the rest won't matter much.
What do you mean in spite of their tech choices? When have the tech choices ever been an issue in the lifespan of Claude Code? From where I sit, it seems like their tech choices enabled them to create an industry-defining product.
I mean people are using Claude Code because of their underlying LLM - they'll put up with Claude Code. There's no other real option to get Opus at a reasonably affordable price without CC.
Most people would choose to swim a lap through a pool of pee to get a billion dollars at the end. The pool of pee itself wasn't the once in a lifetime opportunity (for most).
The criticism didn't appear to me to be that the solution didn't work, just that many of the working solutions we are selecting are dangerously overcomplicated due to shortsighted decisionmaking. The benefits of throwing redundant stacks of abstraction atop each other in terms of time to market are questionable, and obviously absent in every other metric.
So, you have a vibe-coded TUI which happens to work, and then, as a workaround you vibe-translate its engine to make it more performant. Where does that leave you ? Basically, fully dependent on AI to fix whatever breaks. Workaround on a workaround is the way I see it, and it aligns with the AI design mentality in general. For a variety of usecases, this might still be a win in terms of overall cost. But, for software that is intended to be built to last, I dont see this approach working out.
That does seem to be the way many use it. I'd be very surprised if they didn't have to insert a rule to prevent opus from constantly asking why they didn't just use ncurses. I just asked sonnet for design options for a tui to onteract with llms to perform sw dev tasks. After describing the tui it immediately suggested ratatui and crossterm as the tech stack. I feel like they must have ignored even the advice of their own llm to come up with this solution.
Edit, the sonnet question shouldn't be taken as proof, it knows I'm a rust dev.
This reply makes no sense in this context, though. Sure, it exploded in popularity based on whatever random tech choices were made. But now, when apparently they're deciding there's a problem there, why unleash $150k of tokens to rewrite a JS runtime wrapper from Zig to a million lines of rust, rather than simply rewrite Claude Code itself to rust?
They probably should rewrite it in Rust, but also, I think the Bun guy wanted to rewrite it in Rust because he thinks Rust is a better choice for Bun, independent of Bun being used by Claude Code.
This is the “eating yogurt with a hammer” argument. Yes, of course you can do that. Yes, the yogurt gets eaten. It’s just… you see someone eating yogurt with a hammer and it’s hard not to wonder wtf is going on.
This is far less so in this case because this is thier hot path. Everything runs through it and tens of billions in revenue depends on it. It needs to be as fast and solid as possible
...while proving their technology has finally reduced these questions down to what's best, instead of "how much effort will it take to be good enough".
If you have unlimited access to the magical development tool, then why would you not?
> It largely works and it's a massive business success.
You can make anything work when you have enough money to buy and radically change the entire runtime you’re relying on.
One must suspect that if they did not have insane amounts of money to burn, they could have tried other approaches to fixing the problems. Maybe engineering, perhaps.
> But a non-UI developer tool with a rigid API surface contract (and associated tests) will always be easier to trust after a rewrite than a partially tested UI tool with ambiguous functionality.
...I don't think I agree at all. Claude Code is a harness driven by text inputs and keyboard shortcuts. You should be able to have automated tests for that, and an AI agent should be able to drive it easily.
Like, I don't disagree with your overall point, but I think your logic would also preclude porting Bun to Rust.
As an industry we are responsible for making our part good. So yes a business can succeed in spite of bad tech choices, but that doesn’t make it good tech.
This is a useless post-hoc rationalization. "It worked out, so it doesn't matter". You're trying to galaxy brain yourself into ignoring the obvious conclusion.
The point is that if you were starting a new TUI LLM harness today, you would basically use CC's architectural decisions as a guide for what not to do.
I think it makes sense that when you've outlawed competition for many/most users of your product's matching service that you would cheap out on it if you were maximally extractive and took no pride in your work, sure.
But the "coding is mostly solved" narrative kinda doesn't match right? If good, correct, high-performance software is like, free now? Wouldn't you want it to be slick as hell, really reliable, all that? Even a little breakage costs a lot of money at that scale and pricing, it would be better than a wash if you put the magic code thing on the case.
"Claude. Do all employee work. Make no mistake. Notify in slack when revenue is double."
I never knew that running an interactive program in my terminal would absolutely rinse my CPU and battery but that's what Claude, OpenCode and Ghostty have colluded to achieve. Even when the laptop is asleep overnight it's practically melting.
I'm sure there was some logical reason for shoehorning web technology into this stack given that we have a good 40 years or so of experience with interactive terminal programs that use curses/ncurses, alongside emacs, vim, almost the entirety of MS-DOS, and so on.
The fundamental problem with all Js based apps is how they are very single threaded.
With js you get 1 thread at 100% utilization. Power usage and heat scale non-linearly with cpu utilization and 100% utilization on a single threaded js app means you will have ui lag. Other languages like golang would split work across 8 threads and have 8 threads at 20% utilization and this would result in less power usage. Claude Code would have been better off performance wise being an electron app because it would be offloading rendering to the browser and gpu.
Also, the architecture of Open Code is actually a lot better here than Claude Code. ClaudeCode does everything, including rendering in a single thread and it's all in js. OpenCode has a zig based tui renderer it offloads that work onto.
But I will also say these coding agent tuis do get unfairly maligned because they launch subprocesses and those subprocesses tend to be expensive. If you are using Rust analyzer with claude code, it's rust analyzer that's causing the majority of your problems.
No, the fundamental problem of these apps is that they are, for no reason, pretending they need a high powered game engine rendering loop. They don't. It's a text printout of history with some hotkeys for mode switches and such. "rendering in a single thread" should never be an issue because it should never be "rendering". It needs to stream text to stdout. That's been a solved problem for 50 years and now it takes 2GB of memory to be done poorly with broken scrollback.
Drawing to the terminal / rendering / whatever, this is all arguing semantics and very uninteresting and not insightful.
> they need a high powered game engine rendering loop
Don't believe the bs on twitter. Claude code source was leaked, there is no high powered game engine rendering loop.
> It needs to stream text to stdout
These apps are doing real work taking text that is streaming in and doing syntax highlighting, calculating diffs, and rendering markdown. If the work was split across threads they would not use anywhere close to as much power and there would not be a slow ui.
If you think this is actually nothing, prove it. Put the code up on github that shows taking a constant random stream of markdown, code, and diffs and displays it in the terminal can be done cheaply on a single thread.
The reason the computer gets hot and uses more power is because the cpu is getting close to 100% utilization.
> These apps are doing real work taking text that is streaming in and doing syntax highlighting, calculating diffs, and rendering markdown.
The first argument is that these are expensive operations. They are not. And the second argument is the assumption that these are desirable things for an agent system to be doing. That's a personal preference but, personally, I don't want them and would appreciate a way to disable all of that to reduce CPU use.
The argument is that doing it all on a single thread will result in high cpu utilization and that is what makes the power usage spike and the pc feel hot. Thats it.
A lot of people go “js is bad” reflexively and they are right for the wrong reasons. Its not because js (specifically v8) is slow. I have many websites and web based apps open and none fuck up my laptop as hard as claude code.
> If you think this is actually nothing, prove it. Put the code up on github that shows taking a constant random stream of markdown, code, and diffs and displays it in the terminal can be done cheaply on a single thread.
Put up the code and prove it. We already know exactly how fast golang is in comparison to nodejs on basic numeric computations, it's roughly 40 to 50% faster.
That’s not really a big issue. In major OS like the BSD, SMP implementation are not that old. If we can have a full OS running in single core mode, we can have an application being performant too. I’m currently running OpenBSD on 4 cores and it’s basically 99% idle.
It's basically idle because it's not doing anything. If you are streaming in markdown and code and then doing syntax highlighting on this code in real time, then rendering it on the screen you are doing actual work.
It's also all cpu bound work. The majority of the stuff on your screen is being rendered by the gpu.
Of course I have. If I see ghostty constantly consuming the most energy and helping reduce my battery life to barely 2 or 3 hours, the first thing I'm going to do is switch terminal to see if I can improve that situation. The built in terminal and WezTerm have been fine and I've had much more reasonable battery life since.
This does not even speak to it pegging my CPU and keeping the fans running on full blast even when the laptop is supposed to be idle overnight.
This seems a suspicious. How do you measure the CPU load of Ghostty? Is the measure/reporting method just attributing the cpu load of the commands/programs you're running in Ghostty to Ghostty?
You could test this by running "yes > /dev/null" in Ghostty. In Activity Monitor on my Macbook it shows `yes` using 100% and Ghostty using 0.5% of cpu.
If you're looking for a non-ghostty recommendation (not that I have anything against ghostty) I use alacritty + zellij and it works fantastic. It doesn't seem to impact battery, I certainly get good battery usage on both my work and home laptops.
Same. I really want to file a proper bug report for this but I haven't been able to really dig into the details and the last thing I want is a "ghostty is a cpu hog" kind of report without useful info on how to debug that.
As a counter argument - I assume that Anthropic is using AI to write Claude Code.
I've read and heard in videos that Javascript is a pretty good language for AI to write code in. Apparently this is because there is so much training data out there. Also Javascript avoids problems of multi threading and memory management that can mess up the AI in other "more performant" languages.
So maybe Javascript is not the worst choice for writing software fast with AI
I feel like a year ago JavaScript and Python were the best languages for coding agents to use because of their heavier presence in the training data, but I'm not sure that's true any more now.
The latest frontier models are competent at Rust and Swift and all manner of other less widely used languages.
The more important factor is how good they language's compiler is at kicking out actionable error messages, since one-shot code generation isn't as important once you have a coding agent loop.
I recently saw a blog post [1] about a famous Haskel shop moving away from Haskell to Python because the iteration speed with LLMs was just that much better. There is so much React in training data, TS compile times are minimal compared to Rust and similar.
I suspect user facing/fast moving code (UX layer) will move to dynamic systems with fast iteration times. Infra layer will move towards safe systems level environments like Rust. I'm not sure where Java/C# lands in all of this - it's kind of the middle ground between these two worlds but the tradeoffs change drastically with LLMs - my gut feeling says that TS/Python is good enough for UX work and Rust is better for systems work so it gets less popular going forward.
That blog post doesn’t make sense to me at all. The author is going from full modern Haskell (since he mentioned Servant and Beam, you could tell almost every file uses dozens of GHC extensions beyond what Haskell2010 gives you) to Python with dynamic types. He could instead rewrite the Haskell to use less modern type system features and get so much faster compilation speed.
Also GHC has an interpreter. It powers the REPL. No need to compile everything if you’re just experimenting. I do find that in the Haskell world the REPL is criminally underused compared to Python.
And the rest of your comment doesn’t make sense; this shop is rewriting their infra (not UI) from Haskell to Python.
Yknow, I really didn't mind Claude Code that badly, but subjectively speaking I really do like Codex more after using it for a couple weeks. Feels a bit snappier and lighter weight. I know with OpenAI you can actually use third party tools with the subscription so there's less of a draw to using Codex, but I still find myself preferring it now.
Is this because Codex is written in Rust and not JS? I dunno. I think it's more just "lighter" in general, or it certainly feels that way. It's probably possible to make something with a similar feel in JS, just perhaps not with the big honking mess they've created.
Codex appears to be a mildly complex, somewhat-but-not-outrageously-sloppy Rust program (yes, I’ve poked around at its source — thank you OpenAI for making it more or less open source). It has lots of features, mostly related all the fancy web features of Codex.
Claude Code seems to be an insanely complex program will all manner of cutesy features and telemetry features. The net result is approximately the same as Codex, but it’s pretty common in software engineering to find a simple thing and a complex thing that do more or less the same thing.
Why would rewriting Claude code, an app which probably has 30-40 (I might be significantly underestimating) extremely active contributors be easier than rewriting Bun, which has fewer contributors and almost certainly also less lines of code?
Probably because it consumes the same APIs originally developed for a web app and the same front end engineers likely created Claude Code. People assume Anthropic set out to create Code as a product and went through a normal design phase. I think it’s more likely it started as an internal tool or someone’s side project and blew up as a product when they released it to the public.
>I have never once heard a lab or professional say “x model can do anything”
Yeah, they "merely" say that they're about to break the singularity in a couple of years, that it's too capable to be safe to release, that it's going to take 50% (or all, depening on the day and audience) of programmers out of work, that it's smarter than Nobel prize winners, that their programmers don't write anything themselves anymore, and things to that effect.
It’s hyperbolic and intended to generalize the sentiment I perceive from others.
Dario Amodei said in January that he expected software engineers to be replaced [0], so I suppose the quote should be extended to “can do anything… a software engineer can do”
And I think we can all agree that SWE is on the more complex end of all white collar jobs. So, my thinking is that if SWE can hypothetically be replaced, so can many other jobs. Hence, the claim the models can “do anything” intending to capture the majority of white collar work.
This, of course, is if you take their claim at face value - which I certainly do not.
Pointless nitpicking that completely missed my point. Software developers are not the hardest to replace, so your presumption that everything else should be easier is wrong.
I'm doubtful that it has fewer lines of code, but even so, it is almost certainly less tricky and simpler code. You could also rewrite it in a higher level and more forgiving language than Rust (e.g. Go) and get huge improvements. The improvements would probably be much bigger than the improvements they have achieved at the JavaScript runtime level.
Cause it works, most users are fine with it, people don't migrate off it because of the codebase, and easier to maintain if the dev team is familiar with code flow.
This is close to the same "why Spotify is a chromium embed?" question. Because it works, and users are ok with it.
JavaScript is very fast and easy for UI rendering. If it works for web apps it’d also work for the terminal. Sure it’s bloated but it’s fine. The dev velocity of JavaScripts is orders better than rust.
I'm confused as well, could someone who knows how TUIs work explain what's the point of React-style diffing in this context? I thought you need to clean and full redraw if anything changs anyways?
> I thought you need to clean and full redraw if anything changs anyways?
Unless you use an ancient teletype, you don't have to redraw everything. That would make any interactive applications way too slow/flickery.
You can move the cursor arbitrarily in the terminal and start overwriting characters from there. So you need to track state to know what is "dirty" and needs refreshing. Occasionally you issue a full redraw to catch missed artifacts left behind or when the terminal is resized (SIGWINCH).
Otherwise an idle TUI wouldn't halve my laptop's battery life. Maybe that's an exaggeration but not that much, based on looking at wakeups in powertop.
it is kinda mystifying bc from what i understand their engineering ethos is very much "if it's not working, just regenerate it" (which i completely understand).
It's hell to maintain for not much gain (for a use case like this at least). As much as it's become a meme, JS and web tech in general has become extremely portable and stable.
I also don't think Anthropic bought bun to make their TUI better. They could have forked it, they bought bun because it incidentally was excellent for the way agents prefer to work and they wanted to capture that audience.
Probably because claude suggested some kind of wack react based setup early on (because react dominates the training data) and it's be blasphemy worthy of termination for the Anthropic employees to question the sacred pronouncements of the llm.
If you think that way I would recommend just keeping away from these topics. It is just useless arguing and speculating about things don’t matter.
I have been trying to keep away in the last couple weeks and it was all win for me. I still come down here sometimes when I am stressed with real work since it is a strong addiction to see “how terrible the plebs are doing”.
If you are relying on live updates to change state in a dynamic language then you are not doing it "surgically", unless there is some other definition that means hitting it softly with a large rock.
Drilling into the original article where Jarred explained the reasoning behind the change, It's pretty clear that under zig the team was doing things by hand that are automatic in rust.
Humans and agents share one thing: they are both non-deterministic. He talks about the issue of tracking memory lifecycles manually in zig so it can be explicitly freed. As expected, this leads to a long list of bugs where people missed things.
Rust does this automatically. It removes an entire class of errors from his backlog. From an engineering management perspective, this looks like a pretty good trade.
The bonus here is that compiler errors are exactly the kind of deterministic guardrail you need to put around coding agents. Claude works really well if you give it a way to test for correctness and "make it compile" is a pretty good target.
There's a general version of this: the artifact you expose plus the test you run on it. Deterministic tests turn stochastic output into a hard guarantee. Wrote it up here if useful: https://michael.roth.rocks/blog/verification-surface/
Zig (like C) is simply not a good language to use if you're going to do many small allocations with uncorrelated lifetimes. To write robust Zig (or C) code, you must manage lifetimes yourself, for example by grouping allocations on an arena or by having fixed buffers of "things".
You can just do that, and then Zig is really no less robust than Rust. But if you want to do "managed language" style allocation patterns (like what llms generally prefer), it doesn't make sense to use it.
This reads like cope because you're re-inventing RAII from first principles.
I cannot take this seriously as tutorials on robust Zig Allocation Pools will store a deinit method for each item within the pool, so when the pool deinits, all internal objects can be deinit'd.
That is just RAII & dtors from first principles, except with extra overhead of manually storing fat pointers yourself (and the bugs that come with this). Instead of using a language with builtin guarantees & optimizations around handling this so your object pools don't need to carry around a bunch of function pointers. C++ has aggressive de-virtualization passes so at runtime a lot of the 'complex object hierarchies' can be flattened to purely static function calls.
I've argued elsewhere some things that are wrong with RAII and C++ objects in general.
Here I would just like to mention that if you have to rely on "de-virtualization" passes, you're in a miserable situation architecturally. If you have code where the overhead of virtual function calls might be too much to pay, don't do virtual functions then. End of story.
To deconstruct a pool of objects, I don't see what should ever be wrong with a function pointer. The overhead of loading the function pointer will get divided by the number of objects being deconstructed. Care to explain what's the issue here?
1. No, you're not writing code you don't have to. It's not different to implementing this as non-virtual methods, in fact I'd argue doing simple functions is more straightforward.
2. And the code being compiled is abstract & generic, it won't be instantiated for every type and bloat the executable or instruction cache.
3. Security concerns: With C++ virtual methods every object carries a mutable pointer too (to a vtable containing function pointers). What resource management side effects please?
A garbage collected language does this automatically. Rust still requires thinking about and tracking memory lifecycles, but the borrow checker will complain and keep you from doing it wrong. That's why LLMs like Rust. It gives immediate feedback on what to fix. By-default constant reference parameters helps prevent major performance problems.
"At the time of writing, about 4% of Bun's Rust code sits inside an unsafe block (~13,000 unsafe keywords across ~27,000 lines / ~780,000 lines), and 78% of those blocks are a single line — a pointer that came from C++, or one call into a C library. I expect this number to go down over time as we refactor from a faithful Zig port (which had no greppable unsafe keyword) to idiomatic Rust, but we are going to continue using C & C++ libraries like JavaScriptCore so it will always have more unsafe than pure Rust projects."
Personally my take on the entire affair is quite negative, whatever Jarred or Simonw says about it.
I think Bun owned by Anthropic and the entire rewrite with AI is not the real point (even if it's quite interesting, though).
My take is that Jarred, and Bun,didn't demonstrate a serious, adult approach, from "this is my branch, you are overreacting" message to just proceeding with a 1mil+ PR merged in less than month.
The communication is the issue, and it was handled very badly, in a way that impacted trust and divisions.
Was it so difficult to adopt the approach that the TS team adopted for 7.0?
Indeed as much I dislike the approach Bun took, at least the port appears to be working. TS7 is going to cause problems for downstream users because Go is the wrong language to use for something that has to run in WASM.
First, yes, the demand to be able to code natively in a browser is, I have reason to suspect, very large. It's just difficult to measure demand when nobody has ever offered a really compelling product. In engineering terms it's like getting a full-scale reading. The real level could be 1% above a full-scale reading, or the real level could be 100x higher than the full-scale reading.
Secondly, WASM isn't the right target for the browser anyway, JS and the DOM have to be what you consider "native", for the most rigorous UI projects at least (which building an IDE is). If you want to build a cross-platform UI product that doesn't require installation and has Emacs-like levels of extensibility, JS is the end of the line in terms of language selection. There are no other candidates.
> If you want to build a cross-platform UI product that doesn't require installation and has Emacs-like levels of extensibility, JS is the end of the line in terms of language selection. There are no other candidates.
calibre (with python+Qt) begs to differ. And I believe VLC runs on every current platforms. There's also Code::Blocks and Blender. Cross-platform UI is not rocket-science.
All great examples, but ones that do require installation. Their website is just where you download the product, I'm talking about making the website the product.
It's not just typechecking, the typescript library is also the reference parser for TypeScript and reference emit. Emitting JS from TypeScript is non-trivial and non-local.
It's not just in browsers, you might want to run the typescript library on the edge or in some restricted environment where JS/WASM is OK but native code is not.
You may want to use the typescript library as a dependency in your own package. TypeScript becoming non-pure JS means that your library also becomes non-pure JS.
NodeJS can strip types internally without a straight TS dependency. I don’t think this matters, TS was a huge bottleneck for many build pipelines because it never parallelized well
> For me this outputs Bun v1.4.0 (macOS arm64). The most recent release of Bun on GitHub is currently v1.3.14 from May 12th, so that v1.4.0 version number in Claude supports them shipping a preview of a not-yet-released Bun version.
And so, the FOSS project "Bun" silently dies in darkness and is now something completely else. I'm glad I still had "Investigate if Bun is worth it" on my TODO list and hadn't yet gotten to it.
What is the governance structure for Bun by the way? Couldn't find any documents/explanations about how it's supposed to work. I'm guessing it's essentially just "Anthropic decides what gets done and accepted" today?
It’s made absolutely no negative difference, as we’ve seen in the real world in the last 60 days since the merge.
I feel weird having to defend reality; reality being that it was merged nearly 2 months ago and tons of people have had their pitchforks out without a shred of actual evidence that this made bun worse in any measurable way. But they still insist it was a mistake.
I’ve never met Jared or the bun team but I don’t understand all the personal attacks, I just feel the need to correct the facts. Literally who cares what language a JS toolset is written in?
It’s not like they ported JavaScriptCore (the actual JS runtime) to rust even. All that stuff is largely untouched.
>Literally who cares what language a JS toolset is written in?
Maybe you're being coy by asking a rhetorical question you already know the answer to but I'll answer as if you asked sincerely...
There are 2 different groups interacting with software products:
(1) end-users : this is where the "Who cares what language it's written in?!?" is usually applicable. E.g. The finance guys using MS Excel don't care whether it's written in assembly, BASIC, or C Language.
(2) code contributors and/or programming language enthusiasts who see other projects as "validation" of the whatever language they've invested in: these people definitely care.
For all the decades that computer languages have been debated, Group (2) will always discuss projects language choices. E.g. reddit.com switching from Lisp to Python, the Linux kernel fiercely debating future Rust contributions , the Typescript compiler switching from Javascript to Go, Bun switching from Zig to Rust, etc.
People try to lecture others in Group 2 about "don't make a programming language your identity" ... but people are human and they can't look at all the above language choices as totally detached observers. They like to talk about it!
If one is a Zig coder that contributed to the previous Bun Zig codebase, we can't expect them to be neutral observers.
I think you're missing group 3, which is the "assume bad faith and/or bad outcome from any possible change to anything, and especially changes to open source projects that can be interpreted as exogenous, e.g. from an acquirer, and especially if that acquirer is a gigantic commercial entity."
There are not nearly enough disenfranchised Bun-on-Zig contributors to make a dent in this conversation. There are lots of Group 3s in every similar convo, for any combination of technology, project, and acquirer you can name.
I think most of the naysayers are in group 3 because there’s a lot of anger but never a single link to a blog post or analysis done by anyone to demonstrate a regression. not one. There are some that analyzed the quality of the initial rust code and use of unsafe but Claude has been chewing through those as I understand.
Afaik, under current US law (Thaler v. Perlmutter 2025^), "the Copyright Act of 1976 requires all eligible work to be authored in the first instance by a human being".
With regards to AI-generated code, this means the copyrightability (at all, not with regard to who owns it) turns on whether or not a human was substantially involved in its creation.
Existing decisions require evidence of pretty heavy and continued human guidance to qualify.+
To wit, autonomous agent created code (prompt -> machine churns for hours -> output) is explicitly not eligible for copyright.
Functionally, this is a double-edged sword.
On the one hand, it means anything coded with autonomous agents by Meta, Google, et al. can be legally reused if it leaks (because no one could hold copyright on it).
On the other hand, it leaves copy-left open source licenses in a weird place. If you convert open source (even MIT/BSD-style) code into something else with an autonomous coding agent... the result has no copyright (nor can ever in the US).
In this instance, Bun was MIT-licensed, no? Then it was shoved mostly-autonomously through an LLM for the port.
Now Bun-Rust is technically still MIT licensed, but if push came to shove it seems like US law's current position is that Bun-Rust would now have no copyright license (because the manner in which it was developed renders it ineligible for copyright).
That's on the copyright side.
On the infringing usage side (i.e. whether you were entitled to shove a copyrighted work into a coding agent to produce something)... that's still TBD.
Couldn't it be argued that Bun-Rust is still MIT licensed, because the old implementation was "in the first instance" authored by a human? All the machine did was translate it.
I think it's the "infringing usage" question that is more interesting. If the LLM trained on GPL-derived code, what does that mean for the end result?
Yeah you could argue that, but it's a messy argument. I'm wiling to imagine that they hadn't used AI to do the rewrite to Rust. It wouldn't have been all that hard to do with plain old syntax tree transformation (my expertise). The trickier question for me is the ownership at the boundary where prompts were turned into Zig code. That is not a process that could have been done with syntax tree transformation: creative freedom was given to the model as to how to do the work at that stage, and so that is the stage at which I'm least sure they could legally defend their claim to ownership.
"If the LLM trained on GPL-derived code, what does that mean for the end result?"
Either it means nothing at all, or it means that a substantial portion of the code produced at some of the world's most valuable companies over the last two and a half years is GPL.
> who cares what language a JS toolset is written in?
Anthropic, apparently, not the least because they blanket-closed all issues submitted before the rewrite. If the language were irrelevant, it shouldn’t matter for the existing unfixed issues.
> blanket-closed all issues submitted before the rewrite
You'll need a citation for that. While I'm still not sure whether Claude Code's issue tracker is worth much (Anthropic doesn't seem to engage with individual issues a while lot), it still has 5k+ open issues ranging back to March 2025. Bun also still has all of its Zig-timeline issues, all 5k+ of them. So what's this about?
imagine being the leadership of the one of most valuable US private companies in the world. then you have to make something called a "pull request" that gets "reviewed" by someone named "Jarred" to make improvements to your stuff. do you see how that is untenable?
the language is relevant for political not technical reasons. you could say, blanket closing the Issues, getting rid of this thing called Jarred from your stack, etc., is really an attack on the GitHub and the GitHub Agitator Lifestyles, which is why so many commenters on Hacker News actually care.
> It’s made absolutely no negative difference, as we’ve seen in the real world in the last 60 days since the merge.
This is even more interesting given that prewar Bun was not a well respected code base. This matters if the code was bad, were the tests bad / not comprehensive as well? If so, the translation to rust whose sole / primary target was test-passing will have a fair amount of undocumented bugs in it.
> poster child for Zig programming language actually being the prime example of How Not To Write Zig Code
Whole classes of bugs WERE fixed by moving to rust. wouldn’t that result in mass closures of classes of bugs that were no longer relevant in rust? What would you prefer?
I would prefer they confirm before closing. It's AI / bot anyway. Instead it's just mass keyword zig = close. The bug can still exist post-port. None of it got "fact-checked".
In fact a lot of "feature requests" like npm compatibility related or missing specs etc ALL also got closed for being "zig" because reproduction and suggested solution were of course zig.
this whole AI era has put the topic of "do we believe actual reality, or what we hoped/assumed/continue to insist would be reality" front and center. Every discussion is like this these days.
Which was completely bonkers -- it happened completely in the open, people were just outraged that something like this happens without asking them and not on a schedule they perceive as adequate. Most of them haven't really grasped what was happening and why. Many still don't.
> What is the governance structure for Bun by the way? Couldn't find any documents/explanations about how it's supposed to work. I'm guessing it's essentially just "Anthropic decides what gets done and accepted" today?
And this is a valid question. You are not "defending reality" by refusing to listen to it.
In summary and based solely on my understanding:
- Jared misled people about the intentions of the migration. It's not the worst thing in the world, but it's certainly worthy of criticism.
- Jared has commented before about locking out human contributors from open source projects. Whether he was making a larger point is irrelevant as his comment stands on its own.
- Other Bun contributors, past and future, outside of those employed by Anthropic, did not and likely will not have equal access to the model Jared used for the rewrite.
Jared, working in the public Bun repository, used tooling not available to his community to experiment with a signficant migration. He dismissed all concerns and told people it's just a bit of fun, and that it shouldn't be taken seriously. Most of the controversy would have been avoided were the experiment done in private.
None of this is a big scandal but questions about the project are entirely justified.
Rust as a language is irrelevant to this discussion, the problem is that bun was vibe coded by a single dude without any open source community involvement. “bun the open source project” is basically dead at that point: don't expect any of the zig enthusiasts who had their code being forcibly rewritten in a language they don't like to follow Jared.
I agree, it's unfortunate the headlines seem to have become 'rewritten in Rust' (not a bad thing) and not 'vibecoded in a week without review' (a bad thing).
"Vibecoded" is not an accurate description of what actually happened. LLMs are extremely good at porting code from one language to another while preserving semantics. Which is why how everything turned out so well was not very surprising.
The Zig one uses raw pointers. These are bad and get out of hand quickly but at least don't have constraints like "you must never have two &mut on the same value". You may refer to c2rust to see how "semantics preserving transformation" without new UBs looks like.
Rust as a language is not relevant, but the Rust community still helped to popularize the idea that trashing a community by a rewrite is ok if it serves some "higher goal". This rewrite is just a striking example why this is problematic.
Reviewing is meaningless while they are still keeping the 10433 (sorry it has become 10503 since last week) unsafe blocks, most unsound and none encapsulated.
Any review would get to the simple conclusion that this should not be released before all the obvious bads are sorted out.
I'm not a rust dev. But I've been once asked to take care of a TypeScript codebase and the thing was littered with so many casts to `any`, you're wondering why they bothered with TypeScript in the first place. Some people do choose tech on a vibe and not any real analysis.
It isn't disabled, it has exclusions. Now that they have it, they can close the gaps. It was literally impossible to have ANY coverage before, now they are mostly, covered and have an avenue for remediation.
I don't understand why folk are having such a hard time understanding why you do large projects in multiple steps? 80/20 rule? Perfect is the enemy of good?
Was nobody here for moving billions of lines of JavaScript to Typescript? It starts with declarations, then turn on type checking gradually inside the codebase: piece by piece until done.
I like Rust and use it full-time professionally. Unsafe is not the same as unsound. Unsound means that the unsafe code is not maintaining the aliasing invariants on references required by the language, and thus undefined behavior can leak into safe code (that is, the safe code can be miscompiled).
Known unsound code should not be merged, let alone released to production. If you have good enough tests and run them under MIRI or ASAN, maybe you can get away with it for a time, but most Rust experts would not sign-off on such a project.
If somebody put a gun to my head and told me to make the best of such a codebase, I would try to figure out how to turn off the LLVM optimizations that assume the Rust references don't alias. With these optimizations this codebase is scarier than most C or C++ code.
My conclusion was formed in my two months long tracking of the repo activities. They have done absolutely nothing in that front. (Well, to be precise they tried to fix exactly one thing that was pointed out but that's it)
> must interface with C code that has no safe interface
Yeah so the sane first step is to create encapsulated, safe interface for them, especially in a project like this. Deno for instance have ~0.2x as many unsafes.
And mind you if you haven't read the code, the vast majority of unsafe blocks in bun are for raw pointer access to local (Rust) objects because their ownership was a mess both before and after the rewrite. Also funnily enough a lot of the access patterns are wrong (in the Rust sense), leading to hundreds of new undefined behaviors.
> be honest and reasonable
Well, well. Talking about dishonest and unreasonable behavior, why is bun releasing a new version before solving any of those glaring issues? I'd remind you the current new version is not an improvement compared to the previous one, both in terms of correctness and maintainability.
Another point of comparison is density of unsafe: the number of unsafe blocks per line of code and/or file. By this metric, Deno has a bit over half the unsafe (because the bun rewrite is significantly more lines of code).
> I'd remind you the current new version is not an improvement compared to the previous one, both in terms of correctness and maintainability.
Except, you know, multiple real companies saying that it is and using it in production. And the fact it closed all known memory leaks. And that nobody has a really pointed to a single actual issue the new version introduced after two months of endless, ceaseless bitching.
I'm also fascinated by all these people upset at Jarred for harming the readability of a codebase they've literally never cared about before it become drama. Bun has almost exclusively been maintained by Oven employees since it's inception.
> Deno for instance have ~0.2x as many unsafes.
A project written ground-up in Rust idiomatically, with a smaller surface area, still has an unsafe footprint within an order of magnitude compared to this automated rewrite from an unsafe language with different practices and known bugs? That's not exactly the slam you think it is.
Is the idea that a code base reset makes something stop being open source? Or that the number of people doing the reset matters?
I don't see why either of those would be true. The project isn't dead just because it's in a different language now, and for liveness purposes it doesn't matter how it got to that different language.
I think the point is that an “open source project” is more than just the code and license, it’s also the community that builds and maintains it.
A fast rewrite of Bun in Rust has effectively alienated most of the people in the Bun community, so in that sense the “open source project” has died. It’s no longer a community project, it’s just become a personal project again.
Just so everyone know, Bun is and has always been owned by a YC funded org with full time employees. The overwhelming majority of commits came from them.
A reset is very different from not being open source any more. If losing most of the community would mark a project dead in open source terms, then every new project would be dead on arrival. And that would just be silly.
I am impartial on the matter, but I think one of the reasons Bun became a thing in the first place was because of Zig attracted a small but very active developer community. Switching from Zig to Rust effectively alienates that community.
I think the Zig people are really just worried that maybe Zig itself is a DOA language before it has even reached 1.0 because it doesn't offer enough over C for any serious use and their flagship project has now abandoned it.
You, by your own admission, haven't even written a single line of Zig despite having ~31 Zig projects on GitHub. I don't think your knowledge of the language is to be trusted in almost any capacity. This might seem harsh but I don't trust someone who's experience with a language amounts to slopping out 30+ repositories and not even engaging with the language normally.
By my own admission I wrote ~100K loc in zig-head. Having a background in linux kernel development of all things I can tell you that Zig is so much better than C or Rust, that I think linux kernel rush to rust is misguided.
I haven't even stated whether I agree with the opinion that Zig is worth it, in fact I do think Zig is worth it for a large set of problems and I wrote Zig for years, I am stating simply that I would never trust anyone who's self-admitting that they don't even write the language they're arguing for when it comes to opinions on whether it's good or not. It's not really about whether Zig is good, it's about someone who doesn't even write the language and doesn't even know it, not having a valuable opinion on it.
Zig is a DOA language for other reasons though. The reason why Rust enthusiasts act so morally superior is because they are:
> Rob Pike, an unsafe guy, may insist that a small language and garbage collection are enough. But the typesafe visionary Grzegorz Wielbodłąński understands the deeper truth: every invalid state permitted by a compiler is a tiny act of civilizational sabotage.
There is no sense pretending anymore that languages with as many gotchas as C and Zig are "simple". Quite simply, they are not. The complexities lie in what's left unspoken, unaddressed, and of course undefined; failure to comprehend these completely can be catastrophic. Rust is so thoroughly and obviously the correct thing that using anything less correct should be taken as a sign of engineering incompetence.
> There is no sense pretending anymore that languages with as many gotchas as C and Zig are "simple". Quite simply, they are not. The complexities lie in what's left unspoken, unaddressed, and of course undefined; failure to comprehend these completely can be catastrophic.
This is where I’ve arrived too. After nearly 20 years of programming I feel done with leaving foot guns lying around. Languages that are full of them, but “fine” as long as you take extreme care are not interesting to me. I’ve started calling this “simple as long as you avoid all the foot guns” idea the sword juggling fallacy[0].
It’s too bad about Zig because it has many nice ideas, in particular allocators, that I hope Rust or some future language will adopt.
There are many things in life that are "fine" only when you take extreme care (knives, cars, industrial machinery,...). The thing is something like C has many usages and you can't just say "use Rust" and be done with it. Using Rust is not cost-free.
I'm not saying "never use C". The thing I dislike is the false dichotomy between "(Zig|C|Go) is simple unlike Rust, which is complex". A statement like that makes it sound like writing correct code in the former is easier when it's, in fact harder.
Yes they stopped caring after C89, Plan 9 C compiler was a mix of C89 with extensions.
Still they are the authors, and withdrawing from WG14, going their own direction with Alef, Limbo, and finally Go, kind of proves the point they considered C done for its original purpose.
If this were true the very small but active community of Zig contributors could just fork it and you could all return to the happy times of not using Bun anyway.
Bun became a thing because it provided some specific benefit to js ecosystem. Zig enabled the rapid development. The people who contributed were definitely helpful but they can still choose to help or not and new people will step up too
Why is that even a thing to object to? You're talking as if you placed stock in the bizarre idea that Anthropic would close source the project and start charging for it.
I wouldn’t use language as strong as OPs but it is against the spirit of FOSS for a corporate owner to use a private prerelease version of their open source software.
I think it’s valid to object to. If 1.4 is good enough to be used by Claude, why not us?
So you wouldn't, for example, after doing a complete ground-up rewrite, perhaps spend a few months dogfooding it to work out the worst bugs before unleashing it upon the public, thus maximizing your initial velocity by minimizing the blast radius and support requests and triage during this phase?
Yeah. One single project that they control. Not thousands of other people's projects breaking, I'm sure with a ton of HN outcry over releasing "this pile of vibe coded slop" upon the poor populace.
You could! You could not release a “pile of vibe coded slop” onto people’s machines. There don’t even appear to be any particular advantages to Claude upgrading early. If there are no one has been made aware of it.
The irony. A company building models and tooling to automatically produce code being attacked for using automatically produced code in the very tools that allow people to automatically produce code, presumably by somebody who wants to use their tools to automatically produce code, possibly because they believe that their approach at ensuring that automatically produced code is properly reviewed by a responsible human has to be more thorough than whatever that company does because of course they were going too fast and thus it can't be good
Have I? I believe I've merely chased them around their moving goalposts. When it's closed source, that's nefarious because "they're not sharing" and that's against the whole spirit of open source. When it's dogfooding with a reduced audience, it's "shoving vibe coded slop on people" (this information gleaned through magical knowledge). When that unfounded assertion is called, lo and behold: It's closed source, so bad bad bad! It's called a logical fallacy for a reason.
But more to your point: Do you believe in "guilty until proven innocent"? Do you believe that they're doing bad things with the bun code, and you can't be convinced otherwise in your judgment of them until they release the code?
More to the point, because you've been chasing them around goalposts, you've both accepted that the question at hand is unknowable precisely because the source isn't available.
> Do you believe in "guilty until proven innocent"? Do you believe that they're doing bad things with the bun code, and you can't be convinced otherwise in your judgment of them until they release the code?
Hell yes, and anyone who trusts one of the AI labs for anything important is insane.
Whether it's their initial mass piracy and then lying about it, dealmaking with the US government, or continually shifting opt-out lines on what they are and aren't training on, they haven't earned the trust to skip the "but verify" step.
Their economic incentives are too transparently aligned with ends at any costs.
You're running a closed source piece of software (claude code), running on an effectively closed source piece of software (bun), both of them updated daily by AI psychosis bros.
At this point, charging is the least of your issues.
It may be available to us, in the form of a git checkout of their public repository.
It's true that we don't know exactly which, and whether or not there are any other changes added on, but that is the case for every single release of Claude Code that has used bun.
It's probably not. I tried to extract the commit hash from the version of bun packaged in claude code. the commit hashes from previous versions resolve, whereas the commit hash for the current 1.4.0 isn't available.
from strings:
bun-v1.4.0
f6d0fcd24abd48061873c2f1a6fb2a67eee487b8
Upgraded.
Welcome to Bun's latest canary build!
This build does have a different way of identifying itself than earlier builds so it's possible this string isn't correct.
(In contrast, earlier builds that I have locally have commit IDs that can be found in the public repo). I don't think it's particularly damning for them to vendor a canary release, mind you.
> The most recent release of Bun on GitHub is currently v1.3.14 from May 12th, so that v1.4.0 version number in Claude supports them shipping a preview of a not-yet-released Bun version.
> And so, the FOSS project "Bun" silently dies
There’s no implication that it’s because of the switch to Rust.
> The objection isn’t to the language. It’s to Claude using a version of Bun that is not available to us.
I was responding to your GP comment. For weeks, it was uproar over the blanket AI move to Rust and now it’s this reason. That’s why I said the goalposts are being moved.
That seems illogical to me. We’re only allowed to have one objection to a project and once that’s used up we can’t air another? FWIW I don’t think people have forgotten the original objection either!
You can; it feels contrived and very social justice warrior/anti Anthropic (which on HN is in of itself almost a meme now). The main reason was because of the blanket AI move which I could understand.
I think your perception of events is pretty heavily affected by personal bias here. Objecting to a hasty AI rewrite of an entire runtime and objecting to violating the spirit of FOSS is “very social justice warrior”?
Please re read your original comment. AI rewrite is one thing and objecting to FOSS/non FOSS is a new argument, anti-Anthropic etc is moving the goal posts. The main argument was the blanket rewrite to Rust using Claude.
Now, /you/ are trying to move the goalposts into an entirely different argument.
Very likely it’s just anti Anthropic altogether.
Like I said, a meme.
Anthropic hasn’t done anything wrong but if they move a single inch then people will complain. Perhaps it is just a preview version?
Airing two entirely separate objections to a project is not “moving the goalposts”. The original objection still stands! You’re using a phrase you’ve heard in an inappropriate context.
I’m sorry but this is a nonsensical debate.
> Now, /you/ are trying to move the goalposts into an entirely different argument.
You said something and I responded to it. That’s invalid too now? There can only ever be one single objection in a conversation? I’m not permitted to react to the things said? Like I said, nonsense.
> For weeks, it was uproar over the blanket AI move to Rust and now it’s this reason. That’s why I said the goalposts are being moved.
I'm just one person though, and have no problem with a move to language X, using tool Y, who cares?
For "goalpost are being moved" to be valid here, you have to be able to point to someone saying one thing at one point, then same person putting a different target later. You're folding a huge group of people into one person, when that's not really accurate to do.
My overall larger point (maybe poorly stated) was that unless you're engaged specifically in a 1-on-1 conversation with someone, accusing a whole community of "moving the goalpost" makes no sense, there is a whole host of arguments and points being made in different directions all the time, by different individuals.
I see what you are saying. My comment is rooted in the fact that different people are foregrounding different objections to Anthropic/Bun, and taken together it looks like whatever launches, someone will find a reason to be upset
An interesting tidbit is that large parts of the original Bun source code was a line-by-line port of esbuild from Go to Zig (mentioned here: https://bun.com/blog/bun-in-rust), tbh this lowered my respect for the project a bit (a line-by-line port simply isn't as interesting as original work), and it might also explain the subpar Zig code quality (a line-by-line port from Go to Zig simply won't result in idiomatic Zig). It also might explain why porting from Zig to Rust was done 'on a whim', the actual source code (and the idea of 'original work') never seemed to be all that important to the author (and I wouldn't be surprised if the project does more language-hopping in the future heh).
I read your link, written by Bun's author and totally get his thinking.
In the current world of cyber weaknesses everywhere, infrastructure must be solid and rust is a better choice than zig for something like bun.
In other words, bun is not a demo of zig programming that happens to do useful things. Bun does useful things, and must do them securely. That is its number one priority, language is secondary, inasmuch as it helps doing useful things securely.
I don't think the GP had anything to do with the language change itself. More that it marks a clear point of Anthropic taking ownership and governance of the project in a less open direction.
My personal feelings about the matter is that having an LLM rewrite the entire thing as an experiment and then just going with it a few weeks later kills any incentive for a community to build up around it. It's a clear signal that every basic aspect of the runtime can change on a whim.
I don't care about meh Zig being rewritten to bad Rust if it does the same thing, but taking what is presented as" look at this funny experiment I did" and then taking that into production with barely any announcement is what kills off the interest to me.
Bun has been a great ad for whatever LLM they were using but the cool factor is gone now, and that's really what set it apart from basic NodeJS in my mind.
Which community specifically though? The overwhelming “user” community would be web developers and people writing JS/TS, right? Not zig/rust developers.
Developer community. "Open source" historically implied that an interested developer might hack on the code and submit their changes. But if the entire code-base is rewritten by the maintainer every year, then there's no developer community.
There were very many open pull requests from the community that were all invalidated overnight for something that same community was assured was merely an experiment.
The normal process would be "hey, this experiment is going well, we've made this plan, come help us shake out the new codebase for the switchover in X time." None of that happened. There wasn't even an announcement, just a silent commit that trashed hard work from hundreds of community members.
None of that is needed. Nobody benefits from all that time wasting bureaucracy/corpo speak. Bun is quick to deliver new features and bug fixes. With this change, the hope is that'll only get faster.
All those PRs can be fed thru Claude and converted to rust and then manual polish can be added.
Bun is riddled with bugs. That's what moving fast and breaking things gets you. It gets you famously bad codebases that are nightmares to work with and slow you down over time as your sins catch up with you. Vibecoding is not enough.
It's like a couple of languages I know where there's still one real owner, and there's no real review, and PRs are unlikely to be merged, even with review: They might be open source, but it's more a source visible thing, because you are never going to get a change in, and the language will change directions at the creator's lone whim. The best you can get at times is "I didn't like your PR, so I implemented the feature you tried to add completely different". Typical community killers.
> taking that into production with barely any announcement is what kills off the interest to me.
Did Bun v1.4.0 release weeks ago and I missed it? I would call a formal release the point that it goes "into production", and I think dogfooding it via Claude Code is yet another form of testing Bun-in-Rust before the latter goes to casual users.
The language an application is authored in does not matter to me, as a user. I care that it is widely-used (safety in numbers), that it works, and that it is fast.
It's cool that the Zig project exists, but I'm unlikely to ever use Zig so that’s sort of orthogonal to my interests.
> Why does changing to Rust kill the project? I don't understand the point here.
I'm concerned that the complete rewrite in an entirely different language is not a sound technical decision and instead is a ploy to shed copyright claims from past contributors.
Now, based on comments from this thread, the formerly FLOSS project is somehow granting special access to a corporation that apparently is invested in going way out of their way to push implementations that consume the complete rewrite before the world has access to it.
I for one won't be touching Bun. This doesn't pass the smell test. It feels like a bait-and-switch in progress.
> I'm concerned that the complete rewrite in an entirely different language is not a sound technical decision…
Even if this was a terrible technical decision, it is a good, maybe even unavoidable, business decision. And I don’t think moving to Rust was a bad technical decision at all, given Zig is unstable and constantly changing, and that it’s not memory safe, which is a big problem for something like a JS runtime!
The reason it’s a necessary business decision is that Bun is owned by an AI company and Zig has a policy to not accept AI assisted contributions, making it impossible for Anthropic to contribute to a language that is still evolving rapidly, not to mention the bad marketing of using a language that basically is hostile to your product.
I don't care about the language, but pre-releases the community don't get access to but released (Anthropic) applications do have access to, feels a bit too on the nose after the acquisition.
Ok, go ask those people what they think then, I feel no outrage over a project switching language or merging whatever. But when once-semi-transparent projects become more opaque after an acquisition, I'm starting to readjust anything to the project I had in mind.
That PR is the rust rewrite. That's some time in the past now. As of this comment, there is no tagged 1.4 release. This is the present. Anthropic is using apparently a version of Bun that is not publicly available. This is orthogonal to it being Rust-based, as all Bun releases now will be.
That commit (and main) still purports to be 1.3.14, the version numbers haven't changed. Does that not still suggest Anthropic is using something else?
Come on, "not publicly available"? You know how git works right? Each Claude release probably has the HEAD of main compiled as "1.4.0" until there is a real official release.
I do know how git works and in my experience, while the version number sometimes doesn't get bumped until just before a release is tagged, the version number comes from the codebase. If they're building something that says 1.4.0, then they have a codebase that disagrees with ours.
Where is the previous version referred to in the codebase? I'm guessing that would be the place to look for changes.
If you can't find an update at that place in the codebase saying 1.4.0 you can ask where it is. It seems after doing that and not receiving an answer would be the appropriate time to start making the claims that people are throwing around.
Anthropic changed nothing since I wrote published this post a few hours ago - I updated my post to mention Bun canary since it was a point of confusion here on Hacker News.
It's largely just what jarred is willing to accept this week afaik or not, and they did put the bun 1.4.0 version bump in the changelogs for claude code a while ago, over a month almost.
Though most will be forgiven to not reading it since well it's all AI anyways. I don't know how I feel about all this yet, maybe someday.. ooof
Couldn't they have rewritten Claude Code in Rust directly? No more need for a JS runtime, better performance, etc... If their agents can do Zig to Rust, why not JS to Rust?
Well, yeah, it's just good marketing and Bun ultimately doesn't matter anyway, not to the wider ecosystem and especially not to Anthropic. The only purpose Bun had for Anthropic was as a way of getting attention, so that's what they used it for.
In isolation, yes, that does seem like it would have been the better decision for Claude Code, but it also would have severely diminished the value of their Bun/oven.sh acquisition.
Claude Code isn't the only user of Bun (it's probably not even the only user of it internally at Anthropic), and this way they get to keep the Javascript runtime (and other tooling) that their coding models may one day, if not already, prefer to use when given the opportunity. For those kind of apps, you'll probably also eventually find that--what do you know!--Anthropic also has their own cloud offering (instead of Bun being the one to build one) that specializes in running and managing those applications for you. Even if all they get is a community of developers that choose to use Bun over other options, that gives them power and seats at tables they wouldn't have if they just rewrote Claude Code in Rust.
All the emotion of speculations aside, how it runs? It boots faster yeah, but what about RAM and CPU usage? Weird dead loop or dead locks?
If it run as good as before or even better, then that's kinda impressive.
I'm a developer so I really don't like it when AI might took my job, but if everyone on this planet could create a software for themselves exactly as how they wanted with just a few simple demands, that will change the world for the better.
Think of it as a democratization of technology. You don't want Microsoft stealing your data? Just ask a AI to write an OS for you. You don't want Google to listen to what you're saying? Just ask a AI to design a phone for you. If one day the AI ended up doing that, it will be the ultimate technology self-sufficient. In front of that, your job security is insignificant.
It is also why keeping the tech open source is that much important. Otherwise, it's still the same old shit again and again, and, you lose your job too.
It's not even about requirements. It's about responsibility. Someone has to take responsibility for the code and the product. Someone has to hotfix a bug that's costing millions of dollars an hour and someone has to be blamed for a bug that's consting millions of dollars an hour.
Maybe I'm taking crazy pills, but I swore there have been very similar comments I've seen as the current top post by weakfish:
> Maybe I’m taking crazy pills, but I’m still stuck on “why the hell does a TUI need to run in terminal React by way of JavaScript”
> The fact that Anthropic felt the need to buy a runtime so they could make their TUI better speaks more to the quality of engineering than anything else IMO.
> If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.
It turns out, there's some similar sentiments in the last year ish:
Maybe because the 1st thing any experienced technical person would think about? It's like rebuilding and optimizing the racing track to make F1 run faster.
I don't want to edit this to change the narrative, but I wanted to clarify that I'm not not a fan of all of the technologies or people related to this. As far as compan{y,ies} go, though, well..
Anecdotal, but I’ve been getting segfaults in Claude Code. I run inside Kitty tabs, and the entire tab becomes unusable when this happens. No response to inputs at all from that point.
When this happens, a link shows up to report the issue. It’s not clickable (likely due to the segfault), and perhaps more important: it’s encoded, so you can’t see what you would be sending in your report.
Same experience I have with bun in general. As an idea, it's the absolute best js runtime by a very large margin, but in terms of stability it's terrible and segfaults 20x as much as node (I base that number on newrelic telemetry)
I run Ghostty and Claude Code on a work macbook and I haven't seen this yet.
I actually used to have issues with run away memory leaks causing my computer to hang which often required a reboot to recover from. I haven't experienced that in a couple of weeks now. Too early to say just yet but I think its definitely possible that the rust port fixed a bunch of memory leaks that have tangibly improved the experience atleast for me.
What makes you think it's a segfault? Does your shell print "Segmentation fault"? If so, you should be back at your shell and you should be able to recover the tab by typing 'reset' + enter (even if you can't see anything as you're typing it).
If nothing prints "Segmentation fault", this just sounds like a hang
I just had this happen today. It was indeed a segfault.
From what I could tell it looked like it was in JS code that had been JIT compiled. I haven't attempted to troubleshoot further beyond setting all my future Claude Code instances to pipe their stderr to disk so that I don't lose the stack trace next time.
Something similar has been happening to me with Ghostty, but there is no error message or link and it only happens when Claude uses it's interactive questions interface.
It becomes completely unresponsive to any input except scrolling. I can't select options or even cancel out.
Segfaults were a thing with the Zig version. Purely based on the fact it's a line by line translation of the Zig code to unsafe Rust, all the Zig code that caused segfaults is going to also cause segfaults in the Rust version. The Rust code won't fix it until they get to the point of refactoring it into idiomatic and memory safe Rust.
When Go's compiler/runtime was transpiled from C to Go, it resulted in non-idiomatic Go as well. The project is doing fine now, years later... I'm not sure what the fuss is about. Bun is basically using the standard "transpile so that it works and the tests pass => refactor so that it looks idiomatic/nice" technique that's been used many times in other projects that switched languages. The only difference here is that, instead of writing their own transpiler (what the Go team did), they just asked an LLM, which they demonstrated to be a viable approach. This hating on AI for the sake of hating AI is getting ridiculous.
As with all transpile ports, the true test will be how well it can be extended and maintained over time. Historically working with the output of a transpile is not pleasant and requires heavy rework to get it to the point where you can be comfortable enough to extend it.
The existing community is now either going to need to learn Rust or new Rust developers are going to have to join the project and they may not invested enough to refactor the transpiled output when they could work on something else like Boa.
historically we didn’t have LLMs which don’t mind “unpleasant[ness]” and “heavy rework”.
This is I think a preview of the future of software development. LLMs are having the same effect as compilers, frameworks, etc - they are making new kinds of software development feasible which were not previously so.
> historically we didn’t have LLMs which don’t mind “unpleasant[ness]” and “heavy rework”.
I'm not quite as optimistic. "Unpleasantness" might sound like subjective disgust, but it often relates to objective criteria like complexity, that increases the surface area open to bugs in a real way. Similarly, if reworking has a non-0 chance of bugs, its gonna have some form of risk, and a major one will of course be higher.
LLMs may be capable of a lot, and they miggt change what projects people can take on, but they definitely don't write bug free code.
The bun rewrite/transpile did use some neat ideas like lots of testing and per-file translations, so hopefully they have more in their toolbox than "LLMs hopefully won't be affected by complexity or write bugs"
That's a stated goal, so nope. But releasing it before any cleanups is another story.
I'd also like to inform you that
- the current success metrics solely consist of their advertisement, my eyes looking at the code strongly suggest otherwise
- the Bun team lacks knowledge to actually make it more idiomatic: none of the Bun team has written any Rust and relying on model knowledge is already proven insufficient.
The release decision itself is presumably driven by that tbh. It's only LGTM from there when nobody knows how to review unsafe Rust.
> the Bun team lacks knowledge to actually make it more idiomatic: none of the Bun team has written any Rust
Do you know how silly this sounds? Good engineers can work in any language. At the top companies (of which Anthropic is certainly one) they don’t have “C++ engineers” and “rust engineers” they just have engineers.
Yeah I don’t understand this port at all other than as a big marketing stunt.
It would have made far more sense, for reliability, efficiency, cost, etc., every metric really, to use or write a source to source translator that preserves as much structure from the original code as possible. Typically if you do a rewrite there are lessons learned from the existing code base that you want to take into account when doing the rewrite; using a bunch of agents to do the porting file-by-file buys you none of that. In either case the code will be an unidiomatic translation, just with LLMs you get an added source of indeterminism and a huge bill at the end of the month.
This comment inspired me to take a look at the trend of "unsafe" in the Bun code over time since the rewrite PR first landed - here are the commits where that number changed by at least 10:
The original code was one giant unsafe block with almost no tangible way to find or debug all the subtle memory bugs and leaks they had.
Now it's smaller, faster and has fewer bugs. Also its every potential memory issue is neatly annotated by an unsafe block so you can go and refactor them out one by one with confidence.
All this seems like a pretty huge improvement to me. Why is this an abomination in your eyes?
Nope, this is demonstrably false because Rust has its own invariants around its types and the codebase is violating a lot of them.
> every potential memory issue is neatly annotated by an unsafe block
"Potential memory issue" can originate in unsafe blocks and safe code that are able to alternate the input condition of these unsafe blocks. Guess what? That still counts towards 100% in this code base, hence the abomination remark.
> refactor them out one by one
Not as easy as it sounds. They are like threads in a yarn ball, if there are one or two ends visible it's easier to sort them out. The actual situation is more like we have tens of thousands of ends (all the raw pointer code that comes with every shared object), to fix them it's basically a requirement to unwind the whole thing (rewrite all the callees and reorder the data flow as needed, redesigning all the APIs during that).
It's too early to declare it as anything remotely close to a win, optimistically saying.
who claimed that? Are you suggesting that the rewrite did not introduce any new bugs? The correct answer is, by the way, that no one knows since it's millions of lines of code no one has properly read.
> smaller, faster
I thought this has already been debunked. You could just write better zig and make it smaller, faster (and have fewer bugs!)
They’re just wildly successful terrible engineers who can describe problems well and have unlimited token budgets. If they were paying for their own token use, the software would be better, they simply don’t have financial incentive to be more performant.
A dirty secret of AI data centers are that they’re only getting 40-60% efficiency out of their GPU clusters and because the moneygun go brrrrr they just buy more.
You wonder why they’re so afraid of the Chinese competition… they can’t afford to be as wasteful
Incidentally, Claude Code has been very buggy for me lately (much more so than before). Lots of TUI rendering issues causing, e.g., the conversation history to be garbled etc.
I've been (grudgingly) using Claude since February.
When I started, I discovered to my shock that it was by far the worst TUI I had ever touched. Rendering glitches, keyboard input screwups, and just all-around jankiness.
Despite that awful baseline, I have to agree that it's gotten noticably worse in the past week or so.
It's started mangling my terminal sessions somehow, so that not all characters I input are visible in the UI.
Backgrounding it, doing a 'reset', then re-foregrounding seems to fix it.
Of course when I asked it to diagnose the problem, it assured me that Claude has no such big and it must be something else I'm running.
All I'm running is tmux and Claude, though, and the behavior surfaced while I was running Claude.
So, yeah - if they just recently updated Claude to use the Rust rewrite, this increased crappiness might actually be due to that. It does seem to at least roughly correlate.
Every time I resize my window now, the output is completely garbled. I often have to ask it to repeat itself just so I can see what it just said. This isn’t a new thing, but it feels like it’s gotten worse. This is on Windows
I'm far from being anti-AI, but these guys take it way too far IMO. It's straight-up AI slop. Like a real engineer still needs to be in the loop and drive the tool.
a terminal app now has a supply chain long enough to include a runtime acquisition. somewhere between "rewrote it in Rust" and "ship it" someone said "or we could just buy the company"
I am getting into the frontend dev and one thing that I don't understand is why people use bun in the first place? It's not much better preforming, it's not much safer, it's still not 100% compliant. Some tests show it's actually slower than node. Why bother switching, then?
Stdlib includes yaml, sqlite etc so you need to pull in fewer deps, so you can avoid the left-pad/is-even node_modules explosion problem to a greater extent
None of them get any influence on my content. That would hurt my credibility, and my credibility is the reason my site is worth sponsoring in the first place.
Honestly, if OpenAI or Anthropic offered to sponsor I'd probably turn them down. The optics of taking sponsorship from companies that I frequently write about are not great.
Fair, that rules out "Anthropic pays you directly."
But look at your own disclosure page [0]: OpenAI paid you for your time at a GPT-5 preview, and you regularly get early access, embargoed previews, and free API credits from OpenAI, Anthropic, Gemini, and Mistral. So "I've made no money from Anthropic" is narrower than it sounds, access and preferential treatment are compensation too, even if cash didn't directly change hands.
Same goes for the sponsor list. Microsoft is OpenAI's investor and infrastructure (or was anyways, I've got no clue what the status of that is these days), Amazon and Google are both major Anthropic investors, and most of that list runs on Azure, AWS, or GCP, or sells tools built on these labs' models. Taking a Microsoft sponsorship isn't really separate from an OpenAI one, it's just a single hop removed. The entire software ecosystem and all the players in it are entangled in this bubble.
I'm not accusing you of consciously hyping any of them. Your posts are high quality even when I disagree with the contents of them. You often list downsides too, prompt injection, security, slop issues but the throughline still repeats: this is inevitable, get on board. Product-market fit found, November 2025 as the inflection point. That kinda framing shows up again and again throughout all your posts.
It's refreshing that you're upfront about the previews and credits and all that jazz, but surely you understand why some people stay skeptical even with that disclosed as it confirms the access exists.
Whether you realize it or not, I think they are indeed paying you in some sense, which is part of why I'm skeptical when your posts consistently land at the top of HN. Not because the writing isn't good, but because I think the same incentive shaping the coverage probably shapes some of that reach too.
Your comment here is fair, and it's why I take my disclosures seriously.
Nobody is unbiased, no matter how hard they might try. I like to get my information from sources where I understand their motivations, so my approach is to try to make my motivations as clear as possible.
(That's why I spend an unreasonable amount of energy arguing with people on Hacker News who call me a shill!)
> "only covering AI" - don't miss my wildlife photography!
The "ai" tagged posts (2,100+) significantly outnumber "sighting" posts by orders of magnitude. Even searching HN, this post is the very first mention of it.
Perhaps that is why everyone here (except you) overlooks that or why we don't see much more of those sightings posts here either.
Yeah, wildlife photography is a new hobby - it used to be every few months, now it's several times a week.
I would be very surprised if one of my sightings posts made it to Hacker News. Maybe if I manage to snap a photo of an actual pelican perched on a bicycle some time.
I thought it was interesting. I didn't write this with Hacker News in mind.
(I was actually half way through writing about something related, when I thought it would be interesting to see if I could prove that I had the Rust version of Bun on my laptop already.)
The port of Bun, which has >5000 open github issues, is used in Claude Code, which has >11000 open github issues. Do people use Bun in things that are expected to work reliably? Have any such projects tried the upgrade yet?
Did Bun mass-close issues that predated the rewrite? It doesn't look like they did, as the oldest open issue is from 2021 and there are many from 2022, but maybe they did something that killed most of the old issues.
Their (public) project management is horrible, you can find fixed issues unclosed and unfixed issues closed. Not really surprising when that part of the work is completely taken over by LLM agents though.
I love bun - although disliked how Jarred did the conversion.
Project-wise, nothing has changed.
Bun was always great because of the fantastic dx - it was just really easy to use , with stuff like out of the box typescript (unreal that it took so long for node, and it's behind a super long flag, wtf...). And it didnt have the weirdness of deno, it maintained backwards compatability with node api, and it just worked.
But it was never stable. You'd have to be fool to believe that a single project could stably do everything bun covers. It's always been an insane project. It was built on top of zig, a langauge that hasn't reached 1.0, and is constantly changing, and throw in how he was rewriting his own custom zig stuff. Like c'mon, let's apply some common sense here.
For me, little has changed. I am still going to use bun as a nice dev tool, and use node for production.
Anthropic bought Bun, so they kinda, sorta had to make this work. I am sure the cost at $145,000 in Claude time will get some attention.
I am curious how this will work going forward from FOSS perspective. Will humans be allowed to modify the generated code? Only the .md prompts for the agents? Or what?
I despise this era we live in. Pushing rewrites like this upon millions of users, when the Bun rewrite has countless known issues and is likely a security nightmare. Every time I ‘brew outdated’ and I see a wall of updates I die a little inside knowing that most of this code has not been verified or even looked at. Yet we hear about massive supply chain attacks pretty much every week now and we’re still full steam ahead on this vibe coded nightmare. God help us. Claude Code in particular updates sometimes multiple times per day. Like I’m sorry but there is no way all this nonsense is safe.
pi runs in TypeScript and I like it, the target language of the tool, for me, matters only such that I can extend it. I like writing extensions, plugins, things, in TypeScript so I'm cool with that!
Claude Code is closed source, doesn't let me extend it beyond hooks, and these I write in bash anyways.
That all said, why should I bother about this change? Feels like a nothing burger to me, as an end user. This should matter more for those that are internal to Claude Code and Bun developing it.
It is absolutely amazing to me that this ai rewrite work so well, maybe claude is not really that much of a complicated tool to stress the bun runtime but still...
It works well because they had tests, they could compare before and after. Likelihood of issues especially if you transpile to a safer language should be minimal.
Yeah, I noticed. I had Claude write a quick JS script for me a few days ago, it then tried to use Bun to run it. When it couldn't find it, it tried to install it with `sudo pacman`. I had to fucking tell it to use Node instead.
Honestly, I initially thought rewriting an entire codebase with AI would be a huge mistake. After reading this, I'm starting to think I was wrong.
If projects like Bun can be substantially rewritten and shipped to millions of users, it suggests we're entering a very different phase of software development.
Today's AI-generated rewrites may not produce code that humans would consider high quality or maintainable. But I'm beginning to wonder whether that will even matter in a few months. If AI is the primary consumer, maintainer, and refactorer of code, human readability becomes far less important than correctness, performance, and the ability to iterate.
This feels like a shift where software may no longer exist as a long-lived artifact in its current form. Instead of writing and maintaining applications for years, we may generate, adapt, and discard them continuously for each use case.
> But I'm beginning to wonder whether that will even matter in a few months.
At that point, even Bun itself doesn't matter. All intermediate tools don't matter if LLMs can reliably write something large.
The problem is that LLM is not quite there yet. The rewrite was only possible because they mostly stick to 1-to-1 translation resulting in non-idiomatic Rust code. So, what from there? I don't think they can really build up a sane codebase from that state. They only shot themselves with a bigger gun.
> The rewrite was only possible because they mostly stick to 1-to-1 translation resulting in non-idiomatic Rust code.
That’s patently false, just read Jarred’s own blog post describing how that was the first stage only, they went through many more to get the amount of non idiomatic, unsafe Rust code to an acceptable level.
Somebody checked[1], and they discovered that the "stages" past the first had minimal impact on the unsafe blocks count. That's just one metric, but it makes me doubt your claim that there was/is a lot of work put into making the translated code idiomatic Rust.
We'll develop faster and better tech. We'll find resources to feed that. Use that to build better. Access better resources. We'll mine asteroids. We'll harness much more from the sun. The factory must grow.
Is that before or after the earths atmosphere acidifies for humans and our bodies can’t hold enough phosphorus or calcium for basic metabolic tasks? You have until 2050:
> Honestly, I initially thought rewriting an entire codebase with AI would be a huge mistake. After reading this, I'm starting to think I was wrong.
> If projects like Bun can be substantially rewritten and shipped to millions of users, it suggests we're entering a very different phase of software development.
exactly. this wasn't a technical project. this was a marketing stunt that worked on you.
Seeing all the people up in arms that there was an automated rewrite of Bun to Rust has been very revealing and disappointing. Very silly behavior and denial over the inevitable.
It was already written in a very performant language so no significant performance improvements should be expected.
The benefit of a rust rewrite is memory safety improvements, but currently they've just rewritten zig to unsafe rust so they don't have that either yet
The blog claims rust chosen mainly to address memory issues, which rust is a better language for. So, success would simply be less new memory errors / easier to patch old ones.
Claude installer/updater had a high memory usage problem (Gigabytes of resident memory used during a fresh installation of Clade with it's native install.sh script, or during a claude update). This was reported as early as December 2025, see https://github.com/anthropics/claude-code/issues/12327#issue....
I don't think their motivation was primarily user-visible stuff. They backed themselves into a corner by forking Zig, and also were fed up with fixing memory errors.
You wouldn't notice either of those if you were a user, unless you happened to hit one of those bugs.
I've been using Claude Code daily for a fairly large FastAPI project and didn't notice anything unusual around that timeframe. If this really was the Rust runtime underneath, "boring is good" seems like the right outcome.
While everyone here in this forum kept arguing (and fighting and yelling at each other) whether tis moral/right/secure/cheap for ppl to rewrite and ship a major software package with LLMs/agents, one of the main drivers behind AI actually did it, without consulting your opinion, and most same everyone actually slurped this decision without paying a a notice.
Boring is good, but this boring is super massive major thing that happened, and precisely because security is still intact.
I'm looking at this situation strictly as 'What's possible today'. If a 1M lines code rewrite from one language to another goes into production in 1 month, that's a very strong signal that the models are now insanely capable.
My anxiety before merging a 2K lines PR is greatly reduced after 3 frontier models (Fable, 5.6 and kimi K3) finds no issues in it.
Just 6 months ago (Opus 4.6) this was not true, a big PR would have countless number of issues.
Aside from the human drama, the message to all of us is - these things are ready for whatever your imagination can throw at them.
I think that's exactly what Anthropic wanted to communicate.
Maybe I’m taking crazy pills, but I’m still stuck on “why the hell does a TUI need to run in terminal React by way of JavaScript”
The fact that Anthropic felt the need to buy a runtime so they could make their TUI better speaks more to the quality of engineering than anything else IMO.
If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.
It largely works and it's a massive business success. This is the classic engineer asking the 'why this technology?' to what amounts to a business question.
They chose it early on, it works, and it makes obscene amounts of revenue. End of story. That doesn't mean it was the "greatest" choice, or has a perfect technical architecture.
Rewrites are never easy, even the bun rewrite. But a non-UI developer tool with a rigid API surface contract (and associated tests) will always be easier to trust after a rewrite than a partially tested UI tool with ambiguous functionality.
>It largely works and it's a massive business success. This is the classic engineer asking the 'why this technology?' to what amounts to a business question.
Your counter argument would be valid for a 2000 or a 2020 business decision about some tech stack.
But the whole point of their product is that it supposedly nullifies such "business" concerns around the use of technology, by making it cheap and fast to build whatever you like automatically.
That they wont, or worse, couldn't, speaks against that.
> But the whole point of their product is that it supposedly nullifies such "business" concerns around the use of technology, by making it cheap and fast to build whatever you like automatically.
This is a spectrum, it's not just 0% vs 100%. Even Fable frakked up a few things really badly in my professional work (though to its credit after a very detailed 2h chat it self-corrected and fixed all the blunders).
I would also challenge "fast" -- Fable (and I assume Mythos) are wicked fast and efficient and even they can't compensate for f.ex. slow recompilations or test suite reruns or security scans, linters etc.
Reminder that the Bun's Zig-to-Rust rewrite took 11 days with dozens of agents working 24/7 and the author put the cost they'd pay (if they had to pay) at about $168k.
> $168k
Billions of dollars of annual revenue go through Claude Code, and the people who work on it must be a lot of millions in headcount.
The time matters a fair bit, it's probably time someone can't spend breaking things in the name of new features, but if rewriting the stack had even a tiny impact on retention or driving higher usage, it would pay back that $168k.
If only paying the $168k was some sort of a guarantee. Vibing doesn't give you that.
You might get more maintainable code for $168k by hiring humans, but if its something bespoke it isn't going to get you far (or far quickly).
Vibing is straight out gambling right now, the thing is, I don't know who the house is any more.
Yep, same thought. And it seems Anthropic agrees.
The company I work for is about 15mm into what is effectively a rewrite. Just a lone data point…
Millimeters?
can't imagine rewriting a runtime to be easier than a coding harness
It's really not about a PL runtime vs. an agent harness, it's about how spaghetti and complex the code is. I do get your point though.
>Reminder that the Bun's Zig-to-Rust rewrite took 11 days with dozens of agents working 24/7 and the author put the cost they'd pay (if they had to pay) at about $168k.
For an entity like Anthropic that's not even the cost of a single developer for a year. It's closer to what they pay a chef on premises.
That the showstopper for a better Claude agent is that they'd need to pay $168k or event $1M or even $10M in costs, can't be used as an excuse.
Lets see what happens in the future. From my experience cost of maintaining this amount of shitty code explodes pretty quickly. We will see in a few years if SW development in all phases using agents is that much automated and easy as people now predict.
Do you know their entire roadmap? If not, maybe different people prioritize things differently when they see their full strategic position.
How is that relevant to my response?
The argument I responded to argued that cost might be the prohibiting factor. I'm saying that for them, the costs mentioned are negligible.
I don't work for them and I don't know their priorities. I can only speculate they're not okay with it but no idea why exactly.
> Reminder that the Bun's Zig-to-Rust rewrite took 11 days with dozens of agents working 24/7 and the author put the cost they'd pay (if they had to pay) at about $168k.
Does anybody really believe that it only took 11 days, one engineer and $168k in tokens?
It played out in public on the GitHub repository, so yes.
I know what Fable did for just 5x6h sessions, singular agent, for my professional work.
Jarred used many agents and they worked 24/7. It tracks for me.
So yes, I do believe it. What makes you skeptical?
Yeah, this is what I’m trying to get at.
There’s two arguments in competition:
1. LLMs make it cheap (in the time sense) and easy to build
2. Rewrites and/or writing something in a native app or program is harder and more time consuming
I think I am willing to take it as an axiom that a native version of CC would be superior from a user perspective. Performance, etc.
I just don’t see how one can say that building things reliably good is easy now when the company providing these tools can’t even do it well.
>2. Rewrites and/or writing something in a native app or program is harder and more time consuming
Why would it be harder and/or more time consuming rather than the opposite? It's like having full specs and a full test-suite to match against the result you want.
> I just don’t see how one can say that building things reliably good is easy now when the company providing these tools can’t even do it well.
I don't know how you can't see it, to me it's blindingly obvious: risk aversion.
Let's say the risk for a problem is 1%; hell, let's put it at 0.1% even. For a company at this scale even that amount of risk is too much.
I trust Opus/Fable to drive prod database migrations and backfills. I don't trust it with our financial ledger. I trust it with part of the infra. I don't trust it with backups. Etc.
You and others are arguing against a premise that nobody defended, namely "Claude can rewrite everything, for free and with zero mistakes". A bit of a straw man, don't you think?
And that's not even touching the fact that writing a GUI app is difficult for LLMs due to difficulties in it getting feedback and a "feel" whether it delivered what was asked (though I know people are working on it).
> I think I am willing to take it as an axiom that a native version of CC would be superior from a user perspective. Performance, etc.
How does that follow, and from where? I never once noticed any visual jank/lag in the TUI; not in iTerm2, not in Kitty, not in Alacritty, not in WezTerm and not in Ghostty. And even if we exclude those two, me and many other devs are quite fine with a TUI and don't miss a GUI program for everyday coding.
Not saying that our preference is superior -- but it'd be strange to blatantly claim: "for dev purposes, GUI > TUI/CLI".
> by making it cheap and fast to build whatever you like automatically.
Cheaper, but not free (if you don't buy into the marketing promises too much). The bigger the project, the bigger the cost, even with a discount.
At the same time, the early versions weren't very good and you can be sure that any rewrite will also need to be similarly iterated upon until it is also good enough and polished.
If you do that and don't spend enough effort on making it be something polished --> your competitors have a better product and you lose.
If you pause feature development to give enough effort to the initiative, you don't get to add new features quickly enough --> your competitors have a better product and you lose.
Maybe their priorities lay elsewhere, like how I've noticed that the desktop app version of Claude Code has gotten both faster (no 2-4 second lag when switching conversations), more stable and usable over time, to where I enjoy using the models because of it, not in spite of it (though not that they haven't had bumps along the way, like that one cache invalidation issue, or how people didn't like the auto accept timeout thing). I don't doubt that you can get pretty far with gradual patches and improvements, instead of only big rewrites.
Honestly it's really cool for me to see Kimi having their own CLI too, same with OpenCode, Pi, Hermes (well more of an agent than just a coding harness but you get the idea) - there's so many competing solutions out there, each good or bad in unique ways.
Just wish we'd see similarly many GUI solutions, for now OpenCode GUI seems like the one I've settled on (cross platform and supports most models), though it's not exactly ideal either (feels a bit barebones, especially in regards to sub-tasks and progress/plan tracking, even ZCode seems a bit better in that regard, it was actually surprisingly good after they pushed out some updates).
Can't have been that cheap if they thought buying Bun for an undisclosed amount of money was cheaper.
I don't think they bought them just for the claude-code gui harness as it is now. it's to have strategic control over some software runtime they can use to do other things related to verification, deployment, and end to end value delivery. Same reason other companies are buying up dev tools.
How much extra money do you think they would make if Claude Code wasn’t JavaScript?
Right now? Zero.
In 2 years? A well-engineered TUI could be the difference between the Blackberry and the iPhone for all we know.
Perhaps over those two years they'll reach the same conclusion and change the engineering?
Perhaps by then it can be too little, too late, too?
Perhaps.
By the same argument, why does it matter from the technology stack side? It doesn't just nullify the business concerns - it largely nullifies the tech stack concerns. Your preference doesn't matter if you aren't touching the code and the product works for your user base.
>making it cheap and fast to build whatever you like automatically
This can be true, while "nullifies such "business" concerns" can be false. Both are not dependent on each other.
Automation doesn't "nullify business concerns", it just changes them.
> But the whole point of their product is that it supposedly nullifies such "business" concerns around the use of technology, by making it cheap and fast to build whatever you like automatically.
Eventually? I am sure they would agree. Currently it's you (and lots of people like you) who are doing the supposing, not Anthropic.
I have been working all day every day in Claude. I loathe their bug-ridden UI. Every release is a new crop of bugs, sometimes the old ones get fixed, usually not.
Any kind of scrolling back, copying text, using their menu system - basically anything that isn’t typing characters has had/still has unaddressed bugs.
OpenAI shipped a competitive model and I’m over in Codex now. I have yet to hit a bug.
If you’re holding the SOTA crown, people will put up with your buggy mess. As soon as that crown slips your pile of trash becomes a huge liability.
> basically anything that isn’t typing characters has had/still has unaddressed bugs.
Oh, that's buggy too. I just tried Claude Code on win10 powershell, and the first typed character goes in the wrong spot and can't be backspaced.
It is by far the the least reliable program on my machine, and every time I have to interact with it I feel like walking in eggshells.
Oh, and the memory use! I run a lot of concurrent sessions. 3 gigs for a terminal window is ludicrous.
They succeeded in spite of their tech choices. Their model outshone it, which is an extremely rare thing to happen and not something they could've counted on. In any other timeline they could've/would've been hurt by their choices.
It's like "why did you go all in on buying scamcoin 3.0 as your investment strategy?" -- "I 5xed my money! End of story! It was fine!"
> They succeeded in spite of their tech choices.
Or those choices just don't matter, it's fundamentally just "tabs vs spaces".
As much as an enthusiast dev like myself hates it -- this is innately true, way too often.
I am 46 y/o and still excited to code and solve problems with code and I still have trouble to admit to myself sometimes that people make dozens of millions with PHP and the tech hardly matters when you can throw bodies at the problem (and when that throwing of bodies at the problem actually solves it, of course).
> I still have trouble to admit to myself sometimes that people make dozens of millions with PHP
Or many billions. eg. Facebook was originally written in PHP.
As a 52 y/o who cares deeply about software development as an art I don't have trouble admitting that the tech hardly matters relative to the economics, that was obvious to me very early in my career.
I have just never really cared because there has always been a path where you can have a decent career being paid to work on and with good technology in spite of the fact that the technology wasn't important to the economics.
I do fear that the rapid adoption of LLMs will probably cause the path I took to narrow considerably. There will likely be less companies willing to pay people to work on elegant technology when they are all competing against endless code generation machines (and this is assuming software companies can exist at all in this future). But at my age that's more of a concern for younger people than me.
Apply this reasoning to any other industry. Yes the average person is not the judge of the quality of a doctor or engineer. That doesn’t invalidate it. You want a doctor who cares about medicine , not whatever will accomplish a business goal.
Eh, the rendering of Claude Code is genuinely such a mess. I have quit claude code over it because when used as a terminal in PHPStorm it sometimes gets so bad that it becomes hard to use.
This isn't a minor nitpick, it's a pretty major UX issue.
Not saying it's like a massive business downside because I'm just one of a few users, maybe this affects their bottom line a little bit, but probably not by much.
Regardless, switching to pi has been a nice breath of fresh air. It just renders well and smoothly and handles terminal resizes well, which is especially important when used in a terminal window in PHPStorm.
> when used as a terminal in PHPStorm
Truthfully, the terminal in Jetbrains IDEs just isn't that great. It's gotten a lot better with their rewrites (yes, plural) of the last years, especially on Windows, but it can still be pretty dodgy.
That may be so but Claude code certainly has rendering glitches in other terminals too.
You don’t have to use these “tools”.
If they don't matter why isn't GTA6 being built in React?
Tabs vs spaces makes no tradeoffs. Tech choices do
A TUI outputting nothing but text shouldn't consume 70 GB RAM and yet there they were just half a year ago: https://x.com/jarredsumner/status/2026497606575398987
They couldn't even fix flickering in their TUI and their new renderer is complete garbage.
They succeeded despite their tech.
>> They succeeded in spite of their tech choices.
It is rarely the case that technology choice is the make-or-break when it comes to whether a product is successful and achieves widespread adoption. Some choices are less ideal than others, but at the end of the day if you manage to make something that people want, the rest won't matter much.
What do you mean in spite of their tech choices? When have the tech choices ever been an issue in the lifespan of Claude Code? From where I sit, it seems like their tech choices enabled them to create an industry-defining product.
for about half a year claude code had this obnoxious flicker problem. i almost quit and went to codex over it.
I mean people are using Claude Code because of their underlying LLM - they'll put up with Claude Code. There's no other real option to get Opus at a reasonably affordable price without CC.
Most people would choose to swim a lap through a pool of pee to get a billion dollars at the end. The pool of pee itself wasn't the once in a lifetime opportunity (for most).
Sorry, I'm bad at analogies.
I may not be the standard case, but I use Claude Code over Codex, OpenCode, Amp, etc primarily because of the UX, not the models or pricing.
> When have the tech choices ever been an issue in the lifespan of Claude Code?
This is just blatantly ignoring all of the glaring issues Claude Code has had over its lifespan.
I think the point is that people still continued to use it above everything else regardless.
Because there's no legal way to use Claude Code on subscription otherwise
Exactly. Their tech choices were not an issue because other things mattered more to users.
The criticism didn't appear to me to be that the solution didn't work, just that many of the working solutions we are selecting are dangerously overcomplicated due to shortsighted decisionmaking. The benefits of throwing redundant stacks of abstraction atop each other in terms of time to market are questionable, and obviously absent in every other metric.
So, you have a vibe-coded TUI which happens to work, and then, as a workaround you vibe-translate its engine to make it more performant. Where does that leave you ? Basically, fully dependent on AI to fix whatever breaks. Workaround on a workaround is the way I see it, and it aligns with the AI design mentality in general. For a variety of usecases, this might still be a win in terms of overall cost. But, for software that is intended to be built to last, I dont see this approach working out.
Bun was not ported to Rust for performance reasons and its not clear to me how anyone can think it was. The reason they've given is memory safety.
It was ported for vibe reasons.
That does seem to be the way many use it. I'd be very surprised if they didn't have to insert a rule to prevent opus from constantly asking why they didn't just use ncurses. I just asked sonnet for design options for a tui to onteract with llms to perform sw dev tasks. After describing the tui it immediately suggested ratatui and crossterm as the tech stack. I feel like they must have ignored even the advice of their own llm to come up with this solution.
Edit, the sonnet question shouldn't be taken as proof, it knows I'm a rust dev.
They decided on the tech stack for Claude Code over a year and a half ago.
I'm going to guess Anthropic are OK with "fully dependent on AI to fix whatever breaks".
> for sw that is intended to be built to last, I dont see this working out.
the era in which the tech industry built software to last was over long before LLMs, especially VC-backed startups.
Did it really exist? I remember buying games on discs as a kid that had bugs in them that prevented you from actually finishing the game at all.
I'm pretty sure "built to last" was only ever more true in specific contexts, and wasn't particularly more true than today.
The era in which the [VC-backed, SV area] tech industry built software to last was over long before LLMs.
Correct
And the question of “if AI is so amazing, shouldn’t it enable easy development of a native TUI even if JS is easier at first?”
Don’t get me wrong I find great value in coding agents daily. Just finding the hype cycle tiring.
This reply makes no sense in this context, though. Sure, it exploded in popularity based on whatever random tech choices were made. But now, when apparently they're deciding there's a problem there, why unleash $150k of tokens to rewrite a JS runtime wrapper from Zig to a million lines of rust, rather than simply rewrite Claude Code itself to rust?
They probably should rewrite it in Rust, but also, I think the Bun guy wanted to rewrite it in Rust because he thinks Rust is a better choice for Bun, independent of Bun being used by Claude Code.
This is the “eating yogurt with a hammer” argument. Yes, of course you can do that. Yes, the yogurt gets eaten. It’s just… you see someone eating yogurt with a hammer and it’s hard not to wonder wtf is going on.
This is far less so in this case because this is thier hot path. Everything runs through it and tens of billions in revenue depends on it. It needs to be as fast and solid as possible
Claude code still can’t handle scrolling history without corruption. It is embarrassingly broken.
> It largely works and it's a massive business success.
The engineer is suggesting that it could be done cheaper and maybe with better outcome. Ironically, this is a classic business case.
...while proving their technology has finally reduced these questions down to what's best, instead of "how much effort will it take to be good enough".
If you have unlimited access to the magical development tool, then why would you not?
But they haven't.
> It largely works and it's a massive business success.
You can make anything work when you have enough money to buy and radically change the entire runtime you’re relying on.
One must suspect that if they did not have insane amounts of money to burn, they could have tried other approaches to fixing the problems. Maybe engineering, perhaps.
Any choice would have made obscene money in this market. It doesn’t make it a good choice.
> But a non-UI developer tool with a rigid API surface contract (and associated tests) will always be easier to trust after a rewrite than a partially tested UI tool with ambiguous functionality.
...I don't think I agree at all. Claude Code is a harness driven by text inputs and keyboard shortcuts. You should be able to have automated tests for that, and an AI agent should be able to drive it easily.
Like, I don't disagree with your overall point, but I think your logic would also preclude porting Bun to Rust.
> “It largely works”
A ringing endorsement!
As an industry we are responsible for making our part good. So yes a business can succeed in spite of bad tech choices, but that doesn’t make it good tech.
It doesn’t work, it performs horribly and is full of bugs. Serious people use open harnesses.
> It largely works and it's a massive business success.
I'd argue these tech companies got popular because they have good models, nothing else.
Even OpenAI took two years to fix basic chat scrolling.
This is a useless post-hoc rationalization. "It worked out, so it doesn't matter". You're trying to galaxy brain yourself into ignoring the obvious conclusion.
The point is that if you were starting a new TUI LLM harness today, you would basically use CC's architectural decisions as a guide for what not to do.
So Claude isn't great for everything?!?
I think it makes sense that when you've outlawed competition for many/most users of your product's matching service that you would cheap out on it if you were maximally extractive and took no pride in your work, sure.
But the "coding is mostly solved" narrative kinda doesn't match right? If good, correct, high-performance software is like, free now? Wouldn't you want it to be slick as hell, really reliable, all that? Even a little breakage costs a lot of money at that scale and pricing, it would be better than a wash if you put the magic code thing on the case.
"Claude. Do all employee work. Make no mistake. Notify in slack when revenue is double."
I never knew that running an interactive program in my terminal would absolutely rinse my CPU and battery but that's what Claude, OpenCode and Ghostty have colluded to achieve. Even when the laptop is asleep overnight it's practically melting.
I'm sure there was some logical reason for shoehorning web technology into this stack given that we have a good 40 years or so of experience with interactive terminal programs that use curses/ncurses, alongside emacs, vim, almost the entirety of MS-DOS, and so on.
The fundamental problem with all Js based apps is how they are very single threaded.
With js you get 1 thread at 100% utilization. Power usage and heat scale non-linearly with cpu utilization and 100% utilization on a single threaded js app means you will have ui lag. Other languages like golang would split work across 8 threads and have 8 threads at 20% utilization and this would result in less power usage. Claude Code would have been better off performance wise being an electron app because it would be offloading rendering to the browser and gpu.
Also, the architecture of Open Code is actually a lot better here than Claude Code. ClaudeCode does everything, including rendering in a single thread and it's all in js. OpenCode has a zig based tui renderer it offloads that work onto.
But I will also say these coding agent tuis do get unfairly maligned because they launch subprocesses and those subprocesses tend to be expensive. If you are using Rust analyzer with claude code, it's rust analyzer that's causing the majority of your problems.
No, the fundamental problem of these apps is that they are, for no reason, pretending they need a high powered game engine rendering loop. They don't. It's a text printout of history with some hotkeys for mode switches and such. "rendering in a single thread" should never be an issue because it should never be "rendering". It needs to stream text to stdout. That's been a solved problem for 50 years and now it takes 2GB of memory to be done poorly with broken scrollback.
Drawing to the terminal / rendering / whatever, this is all arguing semantics and very uninteresting and not insightful.
> they need a high powered game engine rendering loop
Don't believe the bs on twitter. Claude code source was leaked, there is no high powered game engine rendering loop.
> It needs to stream text to stdout
These apps are doing real work taking text that is streaming in and doing syntax highlighting, calculating diffs, and rendering markdown. If the work was split across threads they would not use anywhere close to as much power and there would not be a slow ui.
If you think this is actually nothing, prove it. Put the code up on github that shows taking a constant random stream of markdown, code, and diffs and displays it in the terminal can be done cheaply on a single thread.
The reason the computer gets hot and uses more power is because the cpu is getting close to 100% utilization.
There are two different arguments here.
> These apps are doing real work taking text that is streaming in and doing syntax highlighting, calculating diffs, and rendering markdown.
The first argument is that these are expensive operations. They are not. And the second argument is the assumption that these are desirable things for an agent system to be doing. That's a personal preference but, personally, I don't want them and would appreciate a way to disable all of that to reduce CPU use.
The argument is that doing it all on a single thread will result in high cpu utilization and that is what makes the power usage spike and the pc feel hot. Thats it.
A lot of people go “js is bad” reflexively and they are right for the wrong reasons. Its not because js (specifically v8) is slow. I have many websites and web based apps open and none fuck up my laptop as hard as claude code.
Stuff doable on a pentium 90, and before that, just slowly.
I don't think any of that seriously counts as real work.
Casey Muratori addressed this years ago with the windows terminal drama, https://github.com/cmuratori/refterm
Sorry, but nope; Golang there would be there a beast doing that in a much, much faster way. Not to mention C/C++ with NCurses.
> If you think this is actually nothing, prove it. Put the code up on github that shows taking a constant random stream of markdown, code, and diffs and displays it in the terminal can be done cheaply on a single thread.
Put up the code and prove it. We already know exactly how fast golang is in comparison to nodejs on basic numeric computations, it's roughly 40 to 50% faster.
https://pierre.computer/writing/on-rendering-diffs
I'm not concerned with CPU use/wakeups while actively using it, but with it sitting idle doing nothing.
That’s not really a big issue. In major OS like the BSD, SMP implementation are not that old. If we can have a full OS running in single core mode, we can have an application being performant too. I’m currently running OpenBSD on 4 cores and it’s basically 99% idle.
Bad coding is just bad coding.
It's basically idle because it's not doing anything. If you are streaming in markdown and code and then doing syntax highlighting on this code in real time, then rendering it on the screen you are doing actual work.
It's also all cpu bound work. The majority of the stuff on your screen is being rendered by the gpu.
Why are you implicating ghostty? Have you compared its CPU usage to any other terminal?
Of course I have. If I see ghostty constantly consuming the most energy and helping reduce my battery life to barely 2 or 3 hours, the first thing I'm going to do is switch terminal to see if I can improve that situation. The built in terminal and WezTerm have been fine and I've had much more reasonable battery life since.
This does not even speak to it pegging my CPU and keeping the fans running on full blast even when the laptop is supposed to be idle overnight.
This seems a suspicious. How do you measure the CPU load of Ghostty? Is the measure/reporting method just attributing the cpu load of the commands/programs you're running in Ghostty to Ghostty?
You could test this by running "yes > /dev/null" in Ghostty. In Activity Monitor on my Macbook it shows `yes` using 100% and Ghostty using 0.5% of cpu.
If you're looking for a non-ghostty recommendation (not that I have anything against ghostty) I use alacritty + zellij and it works fantastic. It doesn't seem to impact battery, I certainly get good battery usage on both my work and home laptops.
Same. I really want to file a proper bug report for this but I haven't been able to really dig into the details and the last thing I want is a "ghostty is a cpu hog" kind of report without useful info on how to debug that.
I don't know if its still the case anymore since 1.3 but Ghostty did have a documented issue with Claude causing resource issues.
I think the author is saying everything that touches llm.
Its so wasteful, but that tracks with the modus operandi of AI companies.
As a counter argument - I assume that Anthropic is using AI to write Claude Code.
I've read and heard in videos that Javascript is a pretty good language for AI to write code in. Apparently this is because there is so much training data out there. Also Javascript avoids problems of multi threading and memory management that can mess up the AI in other "more performant" languages.
So maybe Javascript is not the worst choice for writing software fast with AI
I feel like a year ago JavaScript and Python were the best languages for coding agents to use because of their heavier presence in the training data, but I'm not sure that's true any more now.
The latest frontier models are competent at Rust and Swift and all manner of other less widely used languages.
The more important factor is how good they language's compiler is at kicking out actionable error messages, since one-shot code generation isn't as important once you have a coding agent loop.
I recently saw a blog post [1] about a famous Haskel shop moving away from Haskell to Python because the iteration speed with LLMs was just that much better. There is so much React in training data, TS compile times are minimal compared to Rust and similar.
I suspect user facing/fast moving code (UX layer) will move to dynamic systems with fast iteration times. Infra layer will move towards safe systems level environments like Rust. I'm not sure where Java/C# lands in all of this - it's kind of the middle ground between these two worlds but the tradeoffs change drastically with LLMs - my gut feeling says that TS/Python is good enough for UX work and Rust is better for systems work so it gets less popular going forward.
[1] https://avi.press/posts/2026-07-10-after-7-years-in-producti...
That blog post doesn’t make sense to me at all. The author is going from full modern Haskell (since he mentioned Servant and Beam, you could tell almost every file uses dozens of GHC extensions beyond what Haskell2010 gives you) to Python with dynamic types. He could instead rewrite the Haskell to use less modern type system features and get so much faster compilation speed.
Also GHC has an interpreter. It powers the REPL. No need to compile everything if you’re just experimenting. I do find that in the Haskell world the REPL is criminally underused compared to Python.
And the rest of your comment doesn’t make sense; this shop is rewriting their infra (not UI) from Haskell to Python.
>If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.
Yeah, good question. OpenAI decided to rewrite Codex in Rust about a year ago[0].
In fact, since rewrites are that easy, what do we need Bun for? Why doesn't everybody just port all of their Javascript code into Rust?
[0] https://github.com/openai/codex/discussions/1174
It is kind of mind boggling. They could have chosen anything and decided to implement it in the slowest jankiest way possible.
Proves LLMs don’t help with taste.
Yknow, I really didn't mind Claude Code that badly, but subjectively speaking I really do like Codex more after using it for a couple weeks. Feels a bit snappier and lighter weight. I know with OpenAI you can actually use third party tools with the subscription so there's less of a draw to using Codex, but I still find myself preferring it now.
Is this because Codex is written in Rust and not JS? I dunno. I think it's more just "lighter" in general, or it certainly feels that way. It's probably possible to make something with a similar feel in JS, just perhaps not with the big honking mess they've created.
Codex appears to be a mildly complex, somewhat-but-not-outrageously-sloppy Rust program (yes, I’ve poked around at its source — thank you OpenAI for making it more or less open source). It has lots of features, mostly related all the fancy web features of Codex.
Claude Code seems to be an insanely complex program will all manner of cutesy features and telemetry features. The net result is approximately the same as Codex, but it’s pretty common in software engineering to find a simple thing and a complex thing that do more or less the same thing.
Codex CLI and Grok Build are both in Rust. OpenAI’s web still use react. Previously their CLI was React Ink until they ported most of it to Rust
Why would rewriting Claude code, an app which probably has 30-40 (I might be significantly underestimating) extremely active contributors be easier than rewriting Bun, which has fewer contributors and almost certainly also less lines of code?
Because I’ve been told that Fable can do anything :-)
My question is moreso “why was it ever JS in the first place”
& the cost of a native rewrite would be cheaper than acquiring Bun no matter how you shake it
Probably because it consumes the same APIs originally developed for a web app and the same front end engineers likely created Claude Code. People assume Anthropic set out to create Code as a product and went through a normal design phase. I think it’s more likely it started as an internal tool or someone’s side project and blew up as a product when they released it to the public.
But isn't the point of an API that it abstracts away the language(s) in which your application is written?
>Because I’ve been told that Fable can do anything
I hear some version of this anecdote constantly
yet despite using all these prompting tools since 2019 I have never once heard a lab or professional say “x model can do anything”
Can you provide me whatever specific source you heard for this?
>I have never once heard a lab or professional say “x model can do anything”
Yeah, they "merely" say that they're about to break the singularity in a couple of years, that it's too capable to be safe to release, that it's going to take 50% (or all, depening on the day and audience) of programmers out of work, that it's smarter than Nobel prize winners, that their programmers don't write anything themselves anymore, and things to that effect.
Who is “they?”
Again… provide me a quote from someone doing this every day that says: “they're about to break the singularity in a couple of years”
The only people saying this stuff are random Internet commenters, breathless reporters and reactionaries.
The only person on record for a statement like this was Geoff Hinton about radiologists and he has since walked back his statement
It’s hyperbolic and intended to generalize the sentiment I perceive from others.
Dario Amodei said in January that he expected software engineers to be replaced [0], so I suppose the quote should be extended to “can do anything… a software engineer can do”
And I think we can all agree that SWE is on the more complex end of all white collar jobs. So, my thinking is that if SWE can hypothetically be replaced, so can many other jobs. Hence, the claim the models can “do anything” intending to capture the majority of white collar work.
This, of course, is if you take their claim at face value - which I certainly do not.
[0] https://www.entrepreneur.com/business-news/ai-ceo-says-softw...
Code is the killer app for LLMs so software developers are the easiest to replace.
Code isn’t what the majority of software engineering is.
Pointless nitpicking that completely missed my point. Software developers are not the hardest to replace, so your presumption that everything else should be easier is wrong.
So then nobody actually has ever said that and its explicitly hyperbole
So then its misleading in the extreme to say “I’ve been told AI can do anything”
It amplifies hype when people make claims like this by including hyperbolic statements as though they are reflective of the state of the discussion.
Alright, sure, my bad. I thought it was clear that it was meant tongue in cheek, but I’ll accept it was unclear.
That said, with respect what I clarified, I’m curious your thoughts.
I'm doubtful that it has fewer lines of code, but even so, it is almost certainly less tricky and simpler code. You could also rewrite it in a higher level and more forgiving language than Rust (e.g. Go) and get huge improvements. The improvements would probably be much bigger than the improvements they have achieved at the JavaScript runtime level.
this. /s
I asked this in a thread with a CC author a few months ago (I felt — and hope — very politely, with similar background.) No reply. https://news.ycombinator.com/item?id=46716974
At a guess it's because Boris literally wrote a book on TypeScript: https://www.oreilly.com/library/view/programming-typescript/...
Cause it works, most users are fine with it, people don't migrate off it because of the codebase, and easier to maintain if the dev team is familiar with code flow.
This is close to the same "why Spotify is a chromium embed?" question. Because it works, and users are ok with it.
JavaScript is very fast and easy for UI rendering. If it works for web apps it’d also work for the terminal. Sure it’s bloated but it’s fine. The dev velocity of JavaScripts is orders better than rust.
I'm confused as well, could someone who knows how TUIs work explain what's the point of React-style diffing in this context? I thought you need to clean and full redraw if anything changs anyways?
> I thought you need to clean and full redraw if anything changs anyways?
Unless you use an ancient teletype, you don't have to redraw everything. That would make any interactive applications way too slow/flickery.
You can move the cursor arbitrarily in the terminal and start overwriting characters from there. So you need to track state to know what is "dirty" and needs refreshing. Occasionally you issue a full redraw to catch missed artifacts left behind or when the terminal is resized (SIGWINCH).
You can do damage tracking for TUIs. Printing to the terminal is done by moving the cursor and redrawing the line the cursor is on.
Ncurses is how people used to do it.
Otherwise an idle TUI wouldn't halve my laptop's battery life. Maybe that's an exaggeration but not that much, based on looking at wakeups in powertop.
The answer is those are the tools their lead engineers knew, so they repurposed them rather than learning other paradigms .
it is kinda mystifying bc from what i understand their engineering ethos is very much "if it's not working, just regenerate it" (which i completely understand).
So the code for the web, the desktop app, and the cli where largely similar.
The component trees have to be rewritten, only the non-view related JS code can be reused.
> why not rewrite CC in a native language?
It's hell to maintain for not much gain (for a use case like this at least). As much as it's become a meme, JS and web tech in general has become extremely portable and stable.
I also don't think Anthropic bought bun to make their TUI better. They could have forked it, they bought bun because it incidentally was excellent for the way agents prefer to work and they wanted to capture that audience.
I thought maintenance was free with LLMs???
I think they bought Bun because it was a supply chain risk for them.
Their new flagship product (earning them billions of dollars in revenue per month) was dependent on a platform maintained by a tiny startup.
Buying Bun was a very rational way to reduce that risk, epically since it also got them some top tier engineering talent.
Thinking about that further, I wonder if that was part of the rationale for switching from Zig to Rust that they haven't talked about?
Zig is a much riskier bet for your multi-billion dollar cash cow than Rust is.
But saying that out loud would be rude - they took steps to NOT openly criticize Zig, even after Zig's founder did not show them the same courtesy.
Anything that can be written in JavaScript will be written in JavaScript. That's just how it is it seems.
Lots of devs know how to code in it, and the AI models have more training in JavaScript than any other language.
It's like asking "why does everything run on Windows?" Because everything runs on Windows.
> Maybe I’m taking crazy pills, but I’m still stuck on “why the hell does a TUI need to run in terminal React by way of JavaScript”
No, you are not crazy. They do crazy things with unlimited budget, and still their chat app flickers when using.
They should just port pi-tui from pi coding agent, since they have no clue.
Should have done it in C++ with SDL3.
Probably because claude suggested some kind of wack react based setup early on (because react dominates the training data) and it's be blasphemy worthy of termination for the Anthropic employees to question the sacred pronouncements of the llm.
If you think that way I would recommend just keeping away from these topics. It is just useless arguing and speculating about things don’t matter.
I have been trying to keep away in the last couple weeks and it was all win for me. I still come down here sometimes when I am stressed with real work since it is a strong addiction to see “how terrible the plebs are doing”.
JavaScript is dynamic and supports live reload which means iterations are far faster than would be in a compiled language--even for LLMs.
This is especially useful when you're trying to evaluate behaviors while changing state surgically.
If you are relying on live updates to change state in a dynamic language then you are not doing it "surgically", unless there is some other definition that means hitting it softly with a large rock.
There are several compiled languages with live reloading, including C++.
There's no surgery when you're a company with a trillion dollar hammer and every problem looks like a big ass nail.
Drilling into the original article where Jarred explained the reasoning behind the change, It's pretty clear that under zig the team was doing things by hand that are automatic in rust.
Humans and agents share one thing: they are both non-deterministic. He talks about the issue of tracking memory lifecycles manually in zig so it can be explicitly freed. As expected, this leads to a long list of bugs where people missed things.
Rust does this automatically. It removes an entire class of errors from his backlog. From an engineering management perspective, this looks like a pretty good trade.
The bonus here is that compiler errors are exactly the kind of deterministic guardrail you need to put around coding agents. Claude works really well if you give it a way to test for correctness and "make it compile" is a pretty good target.
There's a general version of this: the artifact you expose plus the test you run on it. Deterministic tests turn stochastic output into a hard guarantee. Wrote it up here if useful: https://michael.roth.rocks/blog/verification-surface/
Zig (like C) is simply not a good language to use if you're going to do many small allocations with uncorrelated lifetimes. To write robust Zig (or C) code, you must manage lifetimes yourself, for example by grouping allocations on an arena or by having fixed buffers of "things".
You can just do that, and then Zig is really no less robust than Rust. But if you want to do "managed language" style allocation patterns (like what llms generally prefer), it doesn't make sense to use it.
This reads like cope because you're re-inventing RAII from first principles.
I cannot take this seriously as tutorials on robust Zig Allocation Pools will store a deinit method for each item within the pool, so when the pool deinits, all internal objects can be deinit'd.
That is just RAII & dtors from first principles, except with extra overhead of manually storing fat pointers yourself (and the bugs that come with this). Instead of using a language with builtin guarantees & optimizations around handling this so your object pools don't need to carry around a bunch of function pointers. C++ has aggressive de-virtualization passes so at runtime a lot of the 'complex object hierarchies' can be flattened to purely static function calls.
I've argued elsewhere some things that are wrong with RAII and C++ objects in general.
Here I would just like to mention that if you have to rely on "de-virtualization" passes, you're in a miserable situation architecturally. If you have code where the overhead of virtual function calls might be too much to pay, don't do virtual functions then. End of story.
To deconstruct a pool of objects, I don't see what should ever be wrong with a function pointer. The overhead of loading the function pointer will get divided by the number of objects being deconstructed. Care to explain what's the issue here?
> I don't see what should ever be wrong with a function pointer. [...]Care to explain what's the issue here?
1. You're writing code you don't have to
2. That adds runtime overhead
3. That when you screw up has non-trivial security & resource management side effects
This is objectively indefeasible in nearly any vaguely professional context.
1. No, you're not writing code you don't have to. It's not different to implementing this as non-virtual methods, in fact I'd argue doing simple functions is more straightforward.
2. And the code being compiled is abstract & generic, it won't be instantiated for every type and bloat the executable or instruction cache.
3. Security concerns: With C++ virtual methods every object carries a mutable pointer too (to a vtable containing function pointers). What resource management side effects please?
> Rust does this automatically.
A garbage collected language does this automatically. Rust still requires thinking about and tracking memory lifecycles, but the borrow checker will complain and keep you from doing it wrong. That's why LLMs like Rust. It gives immediate feedback on what to fix. By-default constant reference parameters helps prevent major performance problems.
> Rust does this automatically. It removes an entire class of errors from his backlog.
Even with the huge amount of "unsafe" rust currently in bun? https://news.ycombinator.com/item?id=48967630
You think it’ll all stay there?
Of course they’ll iterate and remove the unsafe bits which were necessary for the transition
LLMs catch memory bugs quite easily in my experience.
All of this is just a (succesful) marketing stunt by Anthropic.
I seem to recall this Rust rewrite is all "unsafe" meaning it really doesn't automatically eliminate those issues.
Relevant passage from Jarred's post:
"At the time of writing, about 4% of Bun's Rust code sits inside an unsafe block (~13,000 unsafe keywords across ~27,000 lines / ~780,000 lines), and 78% of those blocks are a single line — a pointer that came from C++, or one call into a C library. I expect this number to go down over time as we refactor from a faithful Zig port (which had no greppable unsafe keyword) to idiomatic Rust, but we are going to continue using C & C++ libraries like JavaScriptCore so it will always have more unsafe than pure Rust projects."
Bah.
Personally my take on the entire affair is quite negative, whatever Jarred or Simonw says about it.
I think Bun owned by Anthropic and the entire rewrite with AI is not the real point (even if it's quite interesting, though).
My take is that Jarred, and Bun,didn't demonstrate a serious, adult approach, from "this is my branch, you are overreacting" message to just proceeding with a 1mil+ PR merged in less than month.
The communication is the issue, and it was handled very badly, in a way that impacted trust and divisions.
Was it so difficult to adopt the approach that the TS team adopted for 7.0?
I guess the point is none of it matters, CC users didn't notice or don't care except an exceptionally small minority.
Haha TS7 is the next biggest example of, "Let's just do a line by line port to another language instead of seriously examining our architecture"
This is the correct approach (I dare to say the only correct approach) when porting to another language. You can examining the architecture later.
Indeed as much I dislike the approach Bun took, at least the port appears to be working. TS7 is going to cause problems for downstream users because Go is the wrong language to use for something that has to run in WASM.
> TS7 is going to cause problems for downstream users because Go is the wrong language to use for something that has to run in WASM.
Is there a huge need to run that typechecking on browsers?
First, yes, the demand to be able to code natively in a browser is, I have reason to suspect, very large. It's just difficult to measure demand when nobody has ever offered a really compelling product. In engineering terms it's like getting a full-scale reading. The real level could be 1% above a full-scale reading, or the real level could be 100x higher than the full-scale reading.
Secondly, WASM isn't the right target for the browser anyway, JS and the DOM have to be what you consider "native", for the most rigorous UI projects at least (which building an IDE is). If you want to build a cross-platform UI product that doesn't require installation and has Emacs-like levels of extensibility, JS is the end of the line in terms of language selection. There are no other candidates.
> If you want to build a cross-platform UI product that doesn't require installation and has Emacs-like levels of extensibility, JS is the end of the line in terms of language selection. There are no other candidates.
calibre (with python+Qt) begs to differ. And I believe VLC runs on every current platforms. There's also Code::Blocks and Blender. Cross-platform UI is not rocket-science.
All great examples, but ones that do require installation. Their website is just where you download the product, I'm talking about making the website the product.
Yes, in the Monaco editor (https://microsoft.github.io/monaco-editor/).
It's not just typechecking, the typescript library is also the reference parser for TypeScript and reference emit. Emitting JS from TypeScript is non-trivial and non-local.
It's not just in browsers, you might want to run the typescript library on the edge or in some restricted environment where JS/WASM is OK but native code is not.
You may want to use the typescript library as a dependency in your own package. TypeScript becoming non-pure JS means that your library also becomes non-pure JS.
NodeJS can strip types internally without a straight TS dependency. I don’t think this matters, TS was a huge bottleneck for many build pipelines because it never parallelized well
It is incredibly useful
> For me this outputs Bun v1.4.0 (macOS arm64). The most recent release of Bun on GitHub is currently v1.3.14 from May 12th, so that v1.4.0 version number in Claude supports them shipping a preview of a not-yet-released Bun version.
And so, the FOSS project "Bun" silently dies in darkness and is now something completely else. I'm glad I still had "Investigate if Bun is worth it" on my TODO list and hadn't yet gotten to it.
What is the governance structure for Bun by the way? Couldn't find any documents/explanations about how it's supposed to work. I'm guessing it's essentially just "Anthropic decides what gets done and accepted" today?
Why does changing to Rust kill the project? I don't understand the point here.
It’s made absolutely no negative difference, as we’ve seen in the real world in the last 60 days since the merge.
I feel weird having to defend reality; reality being that it was merged nearly 2 months ago and tons of people have had their pitchforks out without a shred of actual evidence that this made bun worse in any measurable way. But they still insist it was a mistake.
I’ve never met Jared or the bun team but I don’t understand all the personal attacks, I just feel the need to correct the facts. Literally who cares what language a JS toolset is written in?
It’s not like they ported JavaScriptCore (the actual JS runtime) to rust even. All that stuff is largely untouched.
>Literally who cares what language a JS toolset is written in?
Maybe you're being coy by asking a rhetorical question you already know the answer to but I'll answer as if you asked sincerely...
There are 2 different groups interacting with software products:
(1) end-users : this is where the "Who cares what language it's written in?!?" is usually applicable. E.g. The finance guys using MS Excel don't care whether it's written in assembly, BASIC, or C Language.
(2) code contributors and/or programming language enthusiasts who see other projects as "validation" of the whatever language they've invested in: these people definitely care.
For all the decades that computer languages have been debated, Group (2) will always discuss projects language choices. E.g. reddit.com switching from Lisp to Python, the Linux kernel fiercely debating future Rust contributions , the Typescript compiler switching from Javascript to Go, Bun switching from Zig to Rust, etc.
People try to lecture others in Group 2 about "don't make a programming language your identity" ... but people are human and they can't look at all the above language choices as totally detached observers. They like to talk about it!
If one is a Zig coder that contributed to the previous Bun Zig codebase, we can't expect them to be neutral observers.
I think you're missing group 3, which is the "assume bad faith and/or bad outcome from any possible change to anything, and especially changes to open source projects that can be interpreted as exogenous, e.g. from an acquirer, and especially if that acquirer is a gigantic commercial entity."
There are not nearly enough disenfranchised Bun-on-Zig contributors to make a dent in this conversation. There are lots of Group 3s in every similar convo, for any combination of technology, project, and acquirer you can name.
I think most of the naysayers are in group 3 because there’s a lot of anger but never a single link to a blog post or analysis done by anyone to demonstrate a regression. not one. There are some that analyzed the quality of the initial rust code and use of unsafe but Claude has been chewing through those as I understand.
I thought that too but it looks like the usage of unsafe hasn't been trending down over time: https://news.ycombinator.com/item?id=48966569#48967630
It was a PR issue more than anything else. It is also a proxy for Pro AI and Anti AI sentiment.
And for most part I don't think it was communicated well apart from the last blog post.
What about Group x.
You just AI generated 1 millions lines of code claiming it's for safety. Who exactly is to make any kind of security guarantees about this?
What was your safety guarantee pre-rewrite? If CVE scanners and aggregators is your answer, then well, this applies to post-rewrite as well.
Don't forget the group asking really dumb pointless questions like "who legally owns the rewritten code"
Afaik, under current US law (Thaler v. Perlmutter 2025^), "the Copyright Act of 1976 requires all eligible work to be authored in the first instance by a human being".
With regards to AI-generated code, this means the copyrightability (at all, not with regard to who owns it) turns on whether or not a human was substantially involved in its creation.
Existing decisions require evidence of pretty heavy and continued human guidance to qualify.+
To wit, autonomous agent created code (prompt -> machine churns for hours -> output) is explicitly not eligible for copyright.
Functionally, this is a double-edged sword.
On the one hand, it means anything coded with autonomous agents by Meta, Google, et al. can be legally reused if it leaks (because no one could hold copyright on it).
On the other hand, it leaves copy-left open source licenses in a weird place. If you convert open source (even MIT/BSD-style) code into something else with an autonomous coding agent... the result has no copyright (nor can ever in the US).
In this instance, Bun was MIT-licensed, no? Then it was shoved mostly-autonomously through an LLM for the port.
Now Bun-Rust is technically still MIT licensed, but if push came to shove it seems like US law's current position is that Bun-Rust would now have no copyright license (because the manner in which it was developed renders it ineligible for copyright).
That's on the copyright side.
On the infringing usage side (i.e. whether you were entitled to shove a copyrighted work into a coding agent to produce something)... that's still TBD.
^ https://media.cadc.uscourts.gov/opinions/docs/2025/03/23-523...
+ https://garrettham.com/ai-generated-works-copyright/
Couldn't it be argued that Bun-Rust is still MIT licensed, because the old implementation was "in the first instance" authored by a human? All the machine did was translate it.
I think it's the "infringing usage" question that is more interesting. If the LLM trained on GPL-derived code, what does that mean for the end result?
Yeah you could argue that, but it's a messy argument. I'm wiling to imagine that they hadn't used AI to do the rewrite to Rust. It wouldn't have been all that hard to do with plain old syntax tree transformation (my expertise). The trickier question for me is the ownership at the boundary where prompts were turned into Zig code. That is not a process that could have been done with syntax tree transformation: creative freedom was given to the model as to how to do the work at that stage, and so that is the stage at which I'm least sure they could legally defend their claim to ownership.
"If the LLM trained on GPL-derived code, what does that mean for the end result?"
Either it means nothing at all, or it means that a substantial portion of the code produced at some of the world's most valuable companies over the last two and a half years is GPL.
> who cares what language a JS toolset is written in?
Anthropic, apparently, not the least because they blanket-closed all issues submitted before the rewrite. If the language were irrelevant, it shouldn’t matter for the existing unfixed issues.
> blanket-closed all issues submitted before the rewrite
You'll need a citation for that. While I'm still not sure whether Claude Code's issue tracker is worth much (Anthropic doesn't seem to engage with individual issues a while lot), it still has 5k+ open issues ranging back to March 2025. Bun also still has all of its Zig-timeline issues, all 5k+ of them. So what's this about?
imagine being the leadership of the one of most valuable US private companies in the world. then you have to make something called a "pull request" that gets "reviewed" by someone named "Jarred" to make improvements to your stuff. do you see how that is untenable?
the language is relevant for political not technical reasons. you could say, blanket closing the Issues, getting rid of this thing called Jarred from your stack, etc., is really an attack on the GitHub and the GitHub Agitator Lifestyles, which is why so many commenters on Hacker News actually care.
> It’s made absolutely no negative difference, as we’ve seen in the real world in the last 60 days since the merge.
This is even more interesting given that prewar Bun was not a well respected code base. This matters if the code was bad, were the tests bad / not comprehensive as well? If so, the translation to rust whose sole / primary target was test-passing will have a fair amount of undocumented bugs in it.
> poster child for Zig programming language actually being the prime example of How Not To Write Zig Code
https://andrewkelley.me/post/my-thoughts-bun-rust-rewrite.ht...
> that this made bun worse in any measurable way
Issues on GitHub was mass closed claiming zig is no longer relevant without fixing the real issues.
Whole classes of bugs WERE fixed by moving to rust. wouldn’t that result in mass closures of classes of bugs that were no longer relevant in rust? What would you prefer?
I would prefer they confirm before closing. It's AI / bot anyway. Instead it's just mass keyword zig = close. The bug can still exist post-port. None of it got "fact-checked".
In fact a lot of "feature requests" like npm compatibility related or missing specs etc ALL also got closed for being "zig" because reproduction and suggested solution were of course zig.
Again doesn't mean it got "auto fixed".
Except that it hasn’t yet hit the real world, the live release is still 1.13.4, the last Zig version. Anthropic does not operate in the real world.
The canary build has been Rust for over a month, available to anyone. In that time it has been used in production for Claude Code and Prisma Compute.
Not sure why this purely factual post got downvoted. Upvoted it.
this whole AI era has put the topic of "do we believe actual reality, or what we hoped/assumed/continue to insist would be reality" front and center. Every discussion is like this these days.
The outrage was more how the rewrite was communicated and defended, which was objectively poor.
Which was completely bonkers -- it happened completely in the open, people were just outraged that something like this happens without asking them and not on a schedule they perceive as adequate. Most of them haven't really grasped what was happening and why. Many still don't.
The crux is:
> What is the governance structure for Bun by the way? Couldn't find any documents/explanations about how it's supposed to work. I'm guessing it's essentially just "Anthropic decides what gets done and accepted" today?
And this is a valid question. You are not "defending reality" by refusing to listen to it.
In summary and based solely on my understanding:
- Jared misled people about the intentions of the migration. It's not the worst thing in the world, but it's certainly worthy of criticism.
- Jared has commented before about locking out human contributors from open source projects. Whether he was making a larger point is irrelevant as his comment stands on its own.
- Other Bun contributors, past and future, outside of those employed by Anthropic, did not and likely will not have equal access to the model Jared used for the rewrite.
Jared, working in the public Bun repository, used tooling not available to his community to experiment with a signficant migration. He dismissed all concerns and told people it's just a bit of fun, and that it shouldn't be taken seriously. Most of the controversy would have been avoided were the experiment done in private.
None of this is a big scandal but questions about the project are entirely justified.
> I'm guessing it's essentially just "Anthropic decides what gets done and accepted" today?
Similar to the Claude Code 60s timeout incident [1] it could just be "Jarade decides what gets done and accepted"
[1]: https://news.ycombinator.com/item?id=48949942
Sometimes the questions aren't justified, though, like when someone else’s project is someone else’s project.
It seems like when some folks see “open source” they think the project maintainers owe them something.
An open source MIT license of the source code is very different from being the original copyright holder.
Rust as a language is irrelevant to this discussion, the problem is that bun was vibe coded by a single dude without any open source community involvement. “bun the open source project” is basically dead at that point: don't expect any of the zig enthusiasts who had their code being forcibly rewritten in a language they don't like to follow Jared.
“bun the JavaScript runtime ” is not dead though.
I agree, it's unfortunate the headlines seem to have become 'rewritten in Rust' (not a bad thing) and not 'vibecoded in a week without review' (a bad thing).
"Vibecoded" is not an accurate description of what actually happened. LLMs are extremely good at porting code from one language to another while preserving semantics. Which is why how everything turned out so well was not very surprising.
"Preserving semantics" by casting pointers to aliasing refs in Rust, ignoring lints and errors in the process.
Can't help laughing at this point.
I don't know, did the prior vibe-coded Zig code not ever have pointers aliased to data? Might be preserving semantics too well, if anything.
The Zig one uses raw pointers. These are bad and get out of hand quickly but at least don't have constraints like "you must never have two &mut on the same value". You may refer to c2rust to see how "semantics preserving transformation" without new UBs looks like.
Rust as a language is not relevant, but the Rust community still helped to popularize the idea that trashing a community by a rewrite is ok if it serves some "higher goal". This rewrite is just a striking example why this is problematic.
Surely a lot of review has happened in the last two months?
Reviewing is meaningless while they are still keeping the 10433 (sorry it has become 10503 since last week) unsafe blocks, most unsound and none encapsulated.
Any review would get to the simple conclusion that this should not be released before all the obvious bads are sorted out.
This feels like such an absurd, bad faith take I keep hearing.
In Zig, every single memory operation is unsafe.
And Bun must interface with C code that has no safe interface, necessitating a ton of boundary-level unsafe behaviors.
There's too much, sure, but can we at least be honest and reasonable?
What's the point of rewriting it to Rust if you're going to, on purpose, disable the most prominent benefits of using Rust?
I'm not a rust dev. But I've been once asked to take care of a TypeScript codebase and the thing was littered with so many casts to `any`, you're wondering why they bothered with TypeScript in the first place. Some people do choose tech on a vibe and not any real analysis.
It isn't disabled, it has exclusions. Now that they have it, they can close the gaps. It was literally impossible to have ANY coverage before, now they are mostly, covered and have an avenue for remediation.
I don't understand why folk are having such a hard time understanding why you do large projects in multiple steps? 80/20 rule? Perfect is the enemy of good?
Was nobody here for moving billions of lines of JavaScript to Typescript? It starts with declarations, then turn on type checking gradually inside the codebase: piece by piece until done.
I like Rust and use it full-time professionally. Unsafe is not the same as unsound. Unsound means that the unsafe code is not maintaining the aliasing invariants on references required by the language, and thus undefined behavior can leak into safe code (that is, the safe code can be miscompiled).
Known unsound code should not be merged, let alone released to production. If you have good enough tests and run them under MIRI or ASAN, maybe you can get away with it for a time, but most Rust experts would not sign-off on such a project.
If somebody put a gun to my head and told me to make the best of such a codebase, I would try to figure out how to turn off the LLVM optimizations that assume the Rust references don't alias. With these optimizations this codebase is scarier than most C or C++ code.
My conclusion was formed in my two months long tracking of the repo activities. They have done absolutely nothing in that front. (Well, to be precise they tried to fix exactly one thing that was pointed out but that's it)
> must interface with C code that has no safe interface
Yeah so the sane first step is to create encapsulated, safe interface for them, especially in a project like this. Deno for instance have ~0.2x as many unsafes.
And mind you if you haven't read the code, the vast majority of unsafe blocks in bun are for raw pointer access to local (Rust) objects because their ownership was a mess both before and after the rewrite. Also funnily enough a lot of the access patterns are wrong (in the Rust sense), leading to hundreds of new undefined behaviors.
> be honest and reasonable
Well, well. Talking about dishonest and unreasonable behavior, why is bun releasing a new version before solving any of those glaring issues? I'd remind you the current new version is not an improvement compared to the previous one, both in terms of correctness and maintainability.
> Deno for instance have ~0.2x as many unsafes.
Another point of comparison is density of unsafe: the number of unsafe blocks per line of code and/or file. By this metric, Deno has a bit over half the unsafe (because the bun rewrite is significantly more lines of code).
> I'd remind you the current new version is not an improvement compared to the previous one, both in terms of correctness and maintainability.
Except, you know, multiple real companies saying that it is and using it in production. And the fact it closed all known memory leaks. And that nobody has a really pointed to a single actual issue the new version introduced after two months of endless, ceaseless bitching.
I'm also fascinated by all these people upset at Jarred for harming the readability of a codebase they've literally never cared about before it become drama. Bun has almost exclusively been maintained by Oven employees since it's inception.
> Deno for instance have ~0.2x as many unsafes.
A project written ground-up in Rust idiomatically, with a smaller surface area, still has an unsafe footprint within an order of magnitude compared to this automated rewrite from an unsafe language with different practices and known bugs? That's not exactly the slam you think it is.
> bun was vibe coded by a single dude without any open source community involvement.
I think even this is largely beside the point. The acquisition of any project by Big Capital (whether tech or VC) is usually a killing blow.
Is the idea that a code base reset makes something stop being open source? Or that the number of people doing the reset matters?
I don't see why either of those would be true. The project isn't dead just because it's in a different language now, and for liveness purposes it doesn't matter how it got to that different language.
I think the point is that an “open source project” is more than just the code and license, it’s also the community that builds and maintains it.
A fast rewrite of Bun in Rust has effectively alienated most of the people in the Bun community, so in that sense the “open source project” has died. It’s no longer a community project, it’s just become a personal project again.
Just so everyone know, Bun is and has always been owned by a YC funded org with full time employees. The overwhelming majority of commits came from them.
A reset is very different from not being open source any more. If losing most of the community would mark a project dead in open source terms, then every new project would be dead on arrival. And that would just be silly.
That's just like your opinion...? More power to Jared (and anyone else) if they can "vibe code" useful projects like bun.
I am impartial on the matter, but I think one of the reasons Bun became a thing in the first place was because of Zig attracted a small but very active developer community. Switching from Zig to Rust effectively alienates that community.
I think the Zig people are really just worried that maybe Zig itself is a DOA language before it has even reached 1.0 because it doesn't offer enough over C for any serious use and their flagship project has now abandoned it.
Anyone actually using it knows it is better. The C interop is so good that there is no use-case where C is the better option IMHO
You, by your own admission, haven't even written a single line of Zig despite having ~31 Zig projects on GitHub. I don't think your knowledge of the language is to be trusted in almost any capacity. This might seem harsh but I don't trust someone who's experience with a language amounts to slopping out 30+ repositories and not even engaging with the language normally.
By my own admission I wrote ~100K loc in zig-head. Having a background in linux kernel development of all things I can tell you that Zig is so much better than C or Rust, that I think linux kernel rush to rust is misguided.
I haven't even stated whether I agree with the opinion that Zig is worth it, in fact I do think Zig is worth it for a large set of problems and I wrote Zig for years, I am stating simply that I would never trust anyone who's self-admitting that they don't even write the language they're arguing for when it comes to opinions on whether it's good or not. It's not really about whether Zig is good, it's about someone who doesn't even write the language and doesn't even know it, not having a valuable opinion on it.
Industry standards, existing team knowledge, use after free story is the same as C already has.
Zig is a DOA language for other reasons though. The reason why Rust enthusiasts act so morally superior is because they are:
> Rob Pike, an unsafe guy, may insist that a small language and garbage collection are enough. But the typesafe visionary Grzegorz Wielbodłąński understands the deeper truth: every invalid state permitted by a compiler is a tiny act of civilizational sabotage.
https://x.com/typememetics/status/2078572052680790237
There is no sense pretending anymore that languages with as many gotchas as C and Zig are "simple". Quite simply, they are not. The complexities lie in what's left unspoken, unaddressed, and of course undefined; failure to comprehend these completely can be catastrophic. Rust is so thoroughly and obviously the correct thing that using anything less correct should be taken as a sign of engineering incompetence.
> There is no sense pretending anymore that languages with as many gotchas as C and Zig are "simple". Quite simply, they are not. The complexities lie in what's left unspoken, unaddressed, and of course undefined; failure to comprehend these completely can be catastrophic.
This is where I’ve arrived too. After nearly 20 years of programming I feel done with leaving foot guns lying around. Languages that are full of them, but “fine” as long as you take extreme care are not interesting to me. I’ve started calling this “simple as long as you avoid all the foot guns” idea the sword juggling fallacy[0].
It’s too bad about Zig because it has many nice ideas, in particular allocators, that I hope Rust or some future language will adopt.
0: https://hugotunius.se/2026/06/15/the-sword-juggling-fallacy....
yeah rust has no footguns. just dont try to mix clone with iter.
Of course Rust has a few footguns too, that's not my point.
There are many things in life that are "fine" only when you take extreme care (knives, cars, industrial machinery,...). The thing is something like C has many usages and you can't just say "use Rust" and be done with it. Using Rust is not cost-free.
I'm not saying "never use C". The thing I dislike is the false dichotomy between "(Zig|C|Go) is simple unlike Rust, which is complex". A statement like that makes it sound like writing correct code in the former is easier when it's, in fact harder.
There is more to it even, the UNIX and C founders arrived to Go, before retirement, after a few other interactions.
AT&T was the one doing the Cyclone research.
And then we have a bunch of folks assuming they know better about C that its own authors?
> And then we have a bunch of folks assuming they know better about C that its own authors?
Barthes aside, C's changed a lot in the years since they left.
Yes they stopped caring after C89, Plan 9 C compiler was a mix of C89 with extensions.
Still they are the authors, and withdrawing from WG14, going their own direction with Alef, Limbo, and finally Go, kind of proves the point they considered C done for its original purpose.
If this were true the very small but active community of Zig contributors could just fork it and you could all return to the happy times of not using Bun anyway.
Bun became a thing because it provided some specific benefit to js ecosystem. Zig enabled the rapid development. The people who contributed were definitely helpful but they can still choose to help or not and new people will step up too
Emphasis on the FOSS project. The v1.4 mentioned is not (yet?) open source, Claude Code is essentially using a proprietary fork, was GP's point.
You can install it now we with bun upgrade —-canary it something along those lines.
I think you’re missing a word or two.
Based on comments elsethread, I think what was meant is: You can install it now with “bun upgrade --canary”, or something along those lines.
However, people also report that the canary version doesn’t identify itself as version 1.4.
It's extremely obvious what they meant, even if it/or wasn't a common phone autocorrect typo.
And GP is full of shit as the main branch is the v1.4.0. it is not "released" yet as it is not finished. It is available as canary version.
So Anthropic ships with unfinished version of bun.
Doesn’t sound like responsible software deployment
Bun is now mainly the runtime for claude code. All changes will go in to make claude code better.
It's not about making the dev experience better than node, that use-case is now secondary.
The objection isn’t to the language. It’s to Claude using a version of Bun that is not available to us. We don’t know what’s actually in it.
Why is that even a thing to object to? You're talking as if you placed stock in the bizarre idea that Anthropic would close source the project and start charging for it.
Stay your pitchforks.
I wouldn’t use language as strong as OPs but it is against the spirit of FOSS for a corporate owner to use a private prerelease version of their open source software.
I think it’s valid to object to. If 1.4 is good enough to be used by Claude, why not us?
So you wouldn't, for example, after doing a complete ground-up rewrite, perhaps spend a few months dogfooding it to work out the worst bugs before unleashing it upon the public, thus maximizing your initial velocity by minimizing the blast radius and support requests and triage during this phase?
It's Anthropic. I am pretty sure they spent time dogfooding it to Mythos or an even more advanced model.
That might even be the reason why they switched to rust.
Don't worry too much.
> before unleashing it upon the public
…but they have? Claude users are public, no? If they were dogfooding internally I’d agree with you.
Yeah. One single project that they control. Not thousands of other people's projects breaking, I'm sure with a ton of HN outcry over releasing "this pile of vibe coded slop" upon the poor populace.
You just can't win.
> you just can’t win
You could! You could not release a “pile of vibe coded slop” onto people’s machines. There don’t even appear to be any particular advantages to Claude upgrading early. If there are no one has been made aware of it.
The irony. A company building models and tooling to automatically produce code being attacked for using automatically produced code in the very tools that allow people to automatically produce code, presumably by somebody who wants to use their tools to automatically produce code, possibly because they believe that their approach at ensuring that automatically produced code is properly reviewed by a responsible human has to be more thorough than whatever that company does because of course they were going too fast and thus it can't be good
How do you know it's vibe coded slop? Have you seen the source code?
> How do you know it's vibe coded slop? Have you seen the source code?
I believe you've just made your opponent's point for them.
Have I? I believe I've merely chased them around their moving goalposts. When it's closed source, that's nefarious because "they're not sharing" and that's against the whole spirit of open source. When it's dogfooding with a reduced audience, it's "shoving vibe coded slop on people" (this information gleaned through magical knowledge). When that unfounded assertion is called, lo and behold: It's closed source, so bad bad bad! It's called a logical fallacy for a reason.
But more to your point: Do you believe in "guilty until proven innocent"? Do you believe that they're doing bad things with the bun code, and you can't be convinced otherwise in your judgment of them until they release the code?
More to the point, because you've been chasing them around goalposts, you've both accepted that the question at hand is unknowable precisely because the source isn't available.
> Do you believe in "guilty until proven innocent"? Do you believe that they're doing bad things with the bun code, and you can't be convinced otherwise in your judgment of them until they release the code?
Hell yes, and anyone who trusts one of the AI labs for anything important is insane.
Whether it's their initial mass piracy and then lying about it, dealmaking with the US government, or continually shifting opt-out lines on what they are and aren't training on, they haven't earned the trust to skip the "but verify" step.
Their economic incentives are too transparently aligned with ends at any costs.
You're running a closed source piece of software (claude code), running on an effectively closed source piece of software (bun), both of them updated daily by AI psychosis bros.
At this point, charging is the least of your issues.
It may be available to us, in the form of a git checkout of their public repository.
It's true that we don't know exactly which, and whether or not there are any other changes added on, but that is the case for every single release of Claude Code that has used bun.
It's probably not. I tried to extract the commit hash from the version of bun packaged in claude code. the commit hashes from previous versions resolve, whereas the commit hash for the current 1.4.0 isn't available.
from strings:
This build does have a different way of identifying itself than earlier builds so it's possible this string isn't correct.(In contrast, earlier builds that I have locally have commit IDs that can be found in the public repo). I don't think it's particularly damning for them to vendor a canary release, mind you.
That is also true of the rest of their codebase, no?
Moving the goalposts?
No? I think OP’s comment was very clear:
> The most recent release of Bun on GitHub is currently v1.3.14 from May 12th, so that v1.4.0 version number in Claude supports them shipping a preview of a not-yet-released Bun version.
> And so, the FOSS project "Bun" silently dies
There’s no implication that it’s because of the switch to Rust.
> The objection isn’t to the language. It’s to Claude using a version of Bun that is not available to us.
I was responding to your GP comment. For weeks, it was uproar over the blanket AI move to Rust and now it’s this reason. That’s why I said the goalposts are being moved.
That seems illogical to me. We’re only allowed to have one objection to a project and once that’s used up we can’t air another? FWIW I don’t think people have forgotten the original objection either!
You can; it feels contrived and very social justice warrior/anti Anthropic (which on HN is in of itself almost a meme now). The main reason was because of the blanket AI move which I could understand.
I think your perception of events is pretty heavily affected by personal bias here. Objecting to a hasty AI rewrite of an entire runtime and objecting to violating the spirit of FOSS is “very social justice warrior”?
What?
Please re read your original comment. AI rewrite is one thing and objecting to FOSS/non FOSS is a new argument, anti-Anthropic etc is moving the goal posts. The main argument was the blanket rewrite to Rust using Claude.
Now, /you/ are trying to move the goalposts into an entirely different argument.
Very likely it’s just anti Anthropic altogether.
Like I said, a meme.
Anthropic hasn’t done anything wrong but if they move a single inch then people will complain. Perhaps it is just a preview version?
Airing two entirely separate objections to a project is not “moving the goalposts”. The original objection still stands! You’re using a phrase you’ve heard in an inappropriate context.
I’m sorry but this is a nonsensical debate.
> Now, /you/ are trying to move the goalposts into an entirely different argument.
You said something and I responded to it. That’s invalid too now? There can only ever be one single objection in a conversation? I’m not permitted to react to the things said? Like I said, nonsense.
> For weeks, it was uproar over the blanket AI move to Rust and now it’s this reason. That’s why I said the goalposts are being moved.
I'm just one person though, and have no problem with a move to language X, using tool Y, who cares?
For "goalpost are being moved" to be valid here, you have to be able to point to someone saying one thing at one point, then same person putting a different target later. You're folding a huge group of people into one person, when that's not really accurate to do.
https://news.ycombinator.com/item?id=48843352
https://news.ycombinator.com/item?id=48837877
Your point being? None of my comments in either of those state that I'm upset about it moving from Zig to Rust?
I wasn’t referring to you and rather the general sentiment. Hence, goal posts have been moved again comment.
My overall larger point (maybe poorly stated) was that unless you're engaged specifically in a 1-on-1 conversation with someone, accusing a whole community of "moving the goalpost" makes no sense, there is a whole host of arguments and points being made in different directions all the time, by different individuals.
I see what you are saying. My comment is rooted in the fact that different people are foregrounding different objections to Anthropic/Bun, and taken together it looks like whatever launches, someone will find a reason to be upset
Definitely, it was a possible reason why Zig actually matters in the industry.
Now it is a Deno clone, both without anything enticing over node.js.
Yeah same, according to one of the Zig team members, the original source code wasn't all that anyway.
But this is HN, a subsection of which places a high importance on what language something is written in, moreso than what it does (feels like).
An interesting tidbit is that large parts of the original Bun source code was a line-by-line port of esbuild from Go to Zig (mentioned here: https://bun.com/blog/bun-in-rust), tbh this lowered my respect for the project a bit (a line-by-line port simply isn't as interesting as original work), and it might also explain the subpar Zig code quality (a line-by-line port from Go to Zig simply won't result in idiomatic Zig). It also might explain why porting from Zig to Rust was done 'on a whim', the actual source code (and the idea of 'original work') never seemed to be all that important to the author (and I wouldn't be surprised if the project does more language-hopping in the future heh).
I read your link, written by Bun's author and totally get his thinking.
In the current world of cyber weaknesses everywhere, infrastructure must be solid and rust is a better choice than zig for something like bun.
In other words, bun is not a demo of zig programming that happens to do useful things. Bun does useful things, and must do them securely. That is its number one priority, language is secondary, inasmuch as it helps doing useful things securely.
Are you really "doing things securely" when you use as many unsafe blocks as the Rust port of Bun does?
I don't think the GP had anything to do with the language change itself. More that it marks a clear point of Anthropic taking ownership and governance of the project in a less open direction.
I didn't read OP as complaining about the rewrite, but about the (lack of clear) governance after being acquired by Anthropic.
As an open source - community driven project? Have you looked at the repo on github?
Theres thousands of PRs from claude agents or whatever.
Yeah really feels like a worthwhile place to contribute lol.
> As an open source - community driven project? Have you looked at the repo on github?
FOSS as in FOSS - Free and Open Source Software. Has nothing to do with if it's community driven or not, I'm strictly talking about FOSS.
My personal feelings about the matter is that having an LLM rewrite the entire thing as an experiment and then just going with it a few weeks later kills any incentive for a community to build up around it. It's a clear signal that every basic aspect of the runtime can change on a whim.
I don't care about meh Zig being rewritten to bad Rust if it does the same thing, but taking what is presented as" look at this funny experiment I did" and then taking that into production with barely any announcement is what kills off the interest to me.
Bun has been a great ad for whatever LLM they were using but the cool factor is gone now, and that's really what set it apart from basic NodeJS in my mind.
Which community specifically though? The overwhelming “user” community would be web developers and people writing JS/TS, right? Not zig/rust developers.
Developer community. "Open source" historically implied that an interested developer might hack on the code and submit their changes. But if the entire code-base is rewritten by the maintainer every year, then there's no developer community.
There were very many open pull requests from the community that were all invalidated overnight for something that same community was assured was merely an experiment.
The normal process would be "hey, this experiment is going well, we've made this plan, come help us shake out the new codebase for the switchover in X time." None of that happened. There wasn't even an announcement, just a silent commit that trashed hard work from hundreds of community members.
None of that is needed. Nobody benefits from all that time wasting bureaucracy/corpo speak. Bun is quick to deliver new features and bug fixes. With this change, the hope is that'll only get faster.
All those PRs can be fed thru Claude and converted to rust and then manual polish can be added.
Bun is riddled with bugs. That's what moving fast and breaking things gets you. It gets you famously bad codebases that are nightmares to work with and slow you down over time as your sins catch up with you. Vibecoding is not enough.
It's like a couple of languages I know where there's still one real owner, and there's no real review, and PRs are unlikely to be merged, even with review: They might be open source, but it's more a source visible thing, because you are never going to get a change in, and the language will change directions at the creator's lone whim. The best you can get at times is "I didn't like your PR, so I implemented the feature you tried to add completely different". Typical community killers.
> taking that into production with barely any announcement is what kills off the interest to me.
Did Bun v1.4.0 release weeks ago and I missed it? I would call a formal release the point that it goes "into production", and I think dogfooding it via Claude Code is yet another form of testing Bun-in-Rust before the latter goes to casual users.
The language an application is authored in does not matter to me, as a user. I care that it is widely-used (safety in numbers), that it works, and that it is fast.
It's cool that the Zig project exists, but I'm unlikely to ever use Zig so that’s sort of orthogonal to my interests.
> Why does changing to Rust kill the project? I don't understand the point here.
I'm concerned that the complete rewrite in an entirely different language is not a sound technical decision and instead is a ploy to shed copyright claims from past contributors.
Now, based on comments from this thread, the formerly FLOSS project is somehow granting special access to a corporation that apparently is invested in going way out of their way to push implementations that consume the complete rewrite before the world has access to it.
I for one won't be touching Bun. This doesn't pass the smell test. It feels like a bait-and-switch in progress.
> I'm concerned that the complete rewrite in an entirely different language is not a sound technical decision…
Even if this was a terrible technical decision, it is a good, maybe even unavoidable, business decision. And I don’t think moving to Rust was a bad technical decision at all, given Zig is unstable and constantly changing, and that it’s not memory safe, which is a big problem for something like a JS runtime!
The reason it’s a necessary business decision is that Bun is owned by an AI company and Zig has a policy to not accept AI assisted contributions, making it impossible for Anthropic to contribute to a language that is still evolving rapidly, not to mention the bad marketing of using a language that basically is hostile to your product.
A lot of hypotheticals, conjecture, speculation, personal feels devoid of any facts. That somehow kills the project. ok!
of course they also gave away their own claim to be the copyright owner, but that's neither here nor there ; )
I don't care about the language, but pre-releases the community don't get access to but released (Anthropic) applications do have access to, feels a bit too on the nose after the acquisition.
The whole point of the outrage was that 1.4 was merged into main. Publicly. So I’m not sure what you mean.
Everything is in the open: PR #30412
> The whole point of the outrage
Ok, go ask those people what they think then, I feel no outrage over a project switching language or merging whatever. But when once-semi-transparent projects become more opaque after an acquisition, I'm starting to readjust anything to the project I had in mind.
That PR is the rust rewrite. That's some time in the past now. As of this comment, there is no tagged 1.4 release. This is the present. Anthropic is using apparently a version of Bun that is not publicly available. This is orthogonal to it being Rust-based, as all Bun releases now will be.
It's publicly available in the GitHub repository and if you run "bun upgrade --canary" - https://github.com/oven-sh/bun/releases/tag/canary
That commit (and main) still purports to be 1.3.14, the version numbers haven't changed. Does that not still suggest Anthropic is using something else?
I think Bun/Anthropic should document which commit hash their "1.4" as shipped in Claude Code uses.
Come on, "not publicly available"? You know how git works right? Each Claude release probably has the HEAD of main compiled as "1.4.0" until there is a real official release.
I do know how git works and in my experience, while the version number sometimes doesn't get bumped until just before a release is tagged, the version number comes from the codebase. If they're building something that says 1.4.0, then they have a codebase that disagrees with ours.
Where is the previous version referred to in the codebase? I'm guessing that would be the place to look for changes.
If you can't find an update at that place in the codebase saying 1.4.0 you can ask where it is. It seems after doing that and not receiving an answer would be the appropriate time to start making the claims that people are throwing around.
This seems like a candidate
https://github.com/oven-sh/bun/commit/b18bf6d1d0a92238f240bf...
The PR is public, you can build and use it as well. The anthropic team just decided to use it, and you can as well.
> The PR is public
I'm talking about the 1.4.0 release:
> Claude supports them shipping a preview of a not-yet-released Bun version
Maybe Bun/Anthropic fixed this after Simon's initial release of the blog post, but seemingly when we both looked, it wasn't public.
> Update: The Rust version has been released as Bun canary - running bun upgrade --canary will install this release.)
Does `bun upgrade` provide the source code?
Yes, it provides the commits for a "changelog". Canary builds track main closely, 98f664962 is the tip of main.
~$ bun upgrade [2.42s] Upgraded.
Welcome to Bun's latest canary build!
Report any bugs:
Changelog:Isn't the source code in the git repo?
v1.4 hasn't been tagged... No idea what the shipped binary corresponds to.
Yeah, of course Anthropic making the version publicly available AFTER people notice it wasn't public, completely solves the issue ;)
Anthropic changed nothing since I wrote published this post a few hours ago - I updated my post to mention Bun canary since it was a point of confusion here on Hacker News.
Claude Code has shipped Bun 1.4. already more than month ago: https://github.com/anthropics/claude-code/releases?q=bun&exp...
Version was changed in Bun in May 18
https://github.com/oven-sh/bun/commit/b18bf6d1d0a92238f240bf...
So it has been canary since then, most likely, if docs are accurate that latest main is canary.
You seem to be wrong about that
Nevertheless, the principles of open source never demanded more than providing the source upon request.
I had "investigate if bun is worth it" too, and decided not to use it, but instability was one of the reasons. So it feels it was the right move.
It's largely just what jarred is willing to accept this week afaik or not, and they did put the bun 1.4.0 version bump in the changelogs for claude code a while ago, over a month almost.
Though most will be forgiven to not reading it since well it's all AI anyways. I don't know how I feel about all this yet, maybe someday.. ooof
> they did put the bun 1.4.0 version bump in the changelogs for claude code a while ago, over a month almost.
Where? Is see no CHANGELOG in the root. I do see LATEST, last modified 2 months ago, and it says 1.3.14
The Claude Code release notes. Not the Bun release notes: https://github.com/anthropics/claude-code/releases/tag/v2.1....
> Upgraded the bundled Bun runtime to 1.4
(Though that doesn't clarify that this is the Rust rewrite)
Why all the mess with Bun?
Couldn't they have rewritten Claude Code in Rust directly? No more need for a JS runtime, better performance, etc... If their agents can do Zig to Rust, why not JS to Rust?
I know, its so confusing. Its almost as if the bun rewrite to Rust has absolutely fuck all nothing to do with Anthropic's product strategy.
Well, yeah, it's just good marketing and Bun ultimately doesn't matter anyway, not to the wider ecosystem and especially not to Anthropic. The only purpose Bun had for Anthropic was as a way of getting attention, so that's what they used it for.
In isolation, yes, that does seem like it would have been the better decision for Claude Code, but it also would have severely diminished the value of their Bun/oven.sh acquisition.
Claude Code isn't the only user of Bun (it's probably not even the only user of it internally at Anthropic), and this way they get to keep the Javascript runtime (and other tooling) that their coding models may one day, if not already, prefer to use when given the opportunity. For those kind of apps, you'll probably also eventually find that--what do you know!--Anthropic also has their own cloud offering (instead of Bun being the one to build one) that specializes in running and managing those applications for you. Even if all they get is a community of developers that choose to use Bun over other options, that gives them power and seats at tables they wouldn't have if they just rewrote Claude Code in Rust.
That'd be my best guess, anyhow.
Is Claude Code bottlenecked by performance?
I think a JS runtime is fine because the ecosystem of tools is very large and plugins are easy.
All the emotion of speculations aside, how it runs? It boots faster yeah, but what about RAM and CPU usage? Weird dead loop or dead locks?
If it run as good as before or even better, then that's kinda impressive.
I'm a developer so I really don't like it when AI might took my job, but if everyone on this planet could create a software for themselves exactly as how they wanted with just a few simple demands, that will change the world for the better.
Think of it as a democratization of technology. You don't want Microsoft stealing your data? Just ask a AI to write an OS for you. You don't want Google to listen to what you're saying? Just ask a AI to design a phone for you. If one day the AI ended up doing that, it will be the ultimate technology self-sufficient. In front of that, your job security is insignificant.
It is also why keeping the tech open source is that much important. Otherwise, it's still the same old shit again and again, and, you lose your job too.
> I'm a developer
Then you must know that the hardest part of software development is getting clear requirements...
> everyone on this planet could create a software for themselves exactly as how they wanted
Even with perfect AGI this will never happen because people will never be able to express clear requirements
It's not even about requirements. It's about responsibility. Someone has to take responsibility for the code and the product. Someone has to hotfix a bug that's costing millions of dollars an hour and someone has to be blamed for a bug that's consting millions of dollars an hour.
A good tool, in the hands of a skilled craftsman gets great results.
The same tool, in the hands of someone that doesn't know how to handle it? I'll let you finish that
Basically, a good developer can handle the tool better by asking the proper questions, setting good guardrails and tweaking the output where needed
> Think of it as a democratization of technology
Incredibly naive take when these models are closed behind (for now subsidized) paywalls.
This "democratization" argument is so nauseating, seems like the Bun port to Rust as a marketing piece (the primary motivator) sold it well!
It's a "democracy", in which some people (Anthropic and co., and anyone willing to suck up to them) are more equal than others...
It definitely worked as a marketing stunt for sure
Maybe I'm taking crazy pills, but I swore there have been very similar comments I've seen as the current top post by weakfish:
> Maybe I’m taking crazy pills, but I’m still stuck on “why the hell does a TUI need to run in terminal React by way of JavaScript”
> The fact that Anthropic felt the need to buy a runtime so they could make their TUI better speaks more to the quality of engineering than anything else IMO.
> If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.
It turns out, there's some similar sentiments in the last year ish:
https://news.ycombinator.com/item?id=47043325
https://news.ycombinator.com/item?id=47105720
https://news.ycombinator.com/item?id=48001113
https://news.ycombinator.com/item?id=46134570
https://news.ycombinator.com/item?id=46124596
I'm not a fan of any of the technologies, companies, or people related to this. I just couldn't shake the feeling that I've seen similar comments.
September and all.
Maybe because the 1st thing any experienced technical person would think about? It's like rebuilding and optimizing the racing track to make F1 run faster.
I don't want to edit this to change the narrative, but I wanted to clarify that I'm not not a fan of all of the technologies or people related to this. As far as compan{y,ies} go, though, well..
Anecdotal, but I’ve been getting segfaults in Claude Code. I run inside Kitty tabs, and the entire tab becomes unusable when this happens. No response to inputs at all from that point.
When this happens, a link shows up to report the issue. It’s not clickable (likely due to the segfault), and perhaps more important: it’s encoded, so you can’t see what you would be sending in your report.
Hope it gets better.
Same experience I have with bun in general. As an idea, it's the absolute best js runtime by a very large margin, but in terms of stability it's terrible and segfaults 20x as much as node (I base that number on newrelic telemetry)
> but in terms of stability it's terrible and segfaults 20x as much as node (I base that number on newrelic telemetry)
In Chrome or Firefox, a segfault is usually automatic CVE and in most cases a bounty of thousands of dollars…
I run Ghostty and Claude Code on a work macbook and I haven't seen this yet.
I actually used to have issues with run away memory leaks causing my computer to hang which often required a reboot to recover from. I haven't experienced that in a couple of weeks now. Too early to say just yet but I think its definitely possible that the rust port fixed a bunch of memory leaks that have tangibly improved the experience atleast for me.
What makes you think it's a segfault? Does your shell print "Segmentation fault"? If so, you should be back at your shell and you should be able to recover the tab by typing 'reset' + enter (even if you can't see anything as you're typing it).
If nothing prints "Segmentation fault", this just sounds like a hang
I just had this happen today. It was indeed a segfault.
From what I could tell it looked like it was in JS code that had been JIT compiled. I haven't attempted to troubleshoot further beyond setting all my future Claude Code instances to pipe their stderr to disk so that I don't lose the stack trace next time.
Bun does not have its own JIT compiler. Bun uses JSC made by Apple. So your blame should be directed to Apple.
And I can believe you because I’ve seen JavaScript-heavy Safari tabs crash.
Something similar has been happening to me with Ghostty, but there is no error message or link and it only happens when Claude uses it's interactive questions interface.
It becomes completely unresponsive to any input except scrolling. I can't select options or even cancel out.
(I am in no way implying this is related to Bun)
Segfaults were a thing with the Zig version. Purely based on the fact it's a line by line translation of the Zig code to unsafe Rust, all the Zig code that caused segfaults is going to also cause segfaults in the Rust version. The Rust code won't fix it until they get to the point of refactoring it into idiomatic and memory safe Rust.
But if the segfaults are new that implies it’s from the LLM no?
Who said they're new? Also, you can encounter new segfaults in a codebase just by executing code paths you haven't seen before.
It's a transpile. And not even a good one. The generated code is far from idiomatic rust. Some may consider it an abomination.
When Go's compiler/runtime was transpiled from C to Go, it resulted in non-idiomatic Go as well. The project is doing fine now, years later... I'm not sure what the fuss is about. Bun is basically using the standard "transpile so that it works and the tests pass => refactor so that it looks idiomatic/nice" technique that's been used many times in other projects that switched languages. The only difference here is that, instead of writing their own transpiler (what the Go team did), they just asked an LLM, which they demonstrated to be a viable approach. This hating on AI for the sake of hating AI is getting ridiculous.
Seems to be working just fine though?
And like, this is just the beginning of the port. They did a mechanical port basically line by line, next step is to make it idiomatic rust.
I thought by now people would’ve learned to stop betting against this rewrite.
> Seems to be working just fine though?
As with all transpile ports, the true test will be how well it can be extended and maintained over time. Historically working with the output of a transpile is not pleasant and requires heavy rework to get it to the point where you can be comfortable enough to extend it.
The existing community is now either going to need to learn Rust or new Rust developers are going to have to join the project and they may not invested enough to refactor the transpiled output when they could work on something else like Boa.
historically we didn’t have LLMs which don’t mind “unpleasant[ness]” and “heavy rework”.
This is I think a preview of the future of software development. LLMs are having the same effect as compilers, frameworks, etc - they are making new kinds of software development feasible which were not previously so.
> historically we didn’t have LLMs which don’t mind “unpleasant[ness]” and “heavy rework”.
I'm not quite as optimistic. "Unpleasantness" might sound like subjective disgust, but it often relates to objective criteria like complexity, that increases the surface area open to bugs in a real way. Similarly, if reworking has a non-0 chance of bugs, its gonna have some form of risk, and a major one will of course be higher.
LLMs may be capable of a lot, and they miggt change what projects people can take on, but they definitely don't write bug free code.
The bun rewrite/transpile did use some neat ideas like lots of testing and per-file translations, so hopefully they have more in their toolbox than "LLMs hopefully won't be affected by complexity or write bugs"
> next step is to make it idiomatic rust
You can tell what will happen when they release it before sorting out all the new bugs introduced by the not-exactly-line-by-line port.
But Bun did not even release a new version of Bun written in Rust yet. It was still a canary version.
Sorry you think they’re not going to continue developing and improving bun and making it more idiomatic?
Given the success of the port so far and the fact that CC is now running on rust Bun, that seems highly unlikely to me.
That's a stated goal, so nope. But releasing it before any cleanups is another story.
I'd also like to inform you that
- the current success metrics solely consist of their advertisement, my eyes looking at the code strongly suggest otherwise
- the Bun team lacks knowledge to actually make it more idiomatic: none of the Bun team has written any Rust and relying on model knowledge is already proven insufficient.
The release decision itself is presumably driven by that tbh. It's only LGTM from there when nobody knows how to review unsafe Rust.
> the Bun team lacks knowledge to actually make it more idiomatic: none of the Bun team has written any Rust
Do you know how silly this sounds? Good engineers can work in any language. At the top companies (of which Anthropic is certainly one) they don’t have “C++ engineers” and “rust engineers” they just have engineers.
One of the best Django engineers I ever worked with had hardly any Django or Python experience when we hired them, but had done plenty of Rails.
They were up and running and super-productive with Django within a week.
Yeah I don’t understand this port at all other than as a big marketing stunt.
It would have made far more sense, for reliability, efficiency, cost, etc., every metric really, to use or write a source to source translator that preserves as much structure from the original code as possible. Typically if you do a rewrite there are lessons learned from the existing code base that you want to take into account when doing the rewrite; using a bunch of agents to do the porting file-by-file buys you none of that. In either case the code will be an unidiomatic translation, just with LLMs you get an added source of indeterminism and a huge bill at the end of the month.
Can you show some examples of abominable Rust code they have?
LLM code has always been an abomination.
Why not transpile directly into LLVM IR?
I don't think AI or humans are trained well on it.
Is it important to be idiomatic if the project meets its goals around memory safety?
No, but the project does not meet its goals around memory safety. It is usage Rust all the way down with same memory safety issues.
If it's not idiomatic, the memory safety won't be guaranteed.
grep -nr 'unsafe' .
Is all you need to know to consider how much of an abomination it is
This comment inspired me to take a look at the trend of "unsafe" in the Bun code over time since the rewrite PR first landed - here are the commits where that number changed by at least 10:
So not as much cleanup as I had expected!ChatGPT written script for counting here: https://gist.github.com/simonw/b1015bcadcedd1a781cedb7af9cbb...
The original code was one giant unsafe block with almost no tangible way to find or debug all the subtle memory bugs and leaks they had.
Now it's smaller, faster and has fewer bugs. Also its every potential memory issue is neatly annotated by an unsafe block so you can go and refactor them out one by one with confidence.
All this seems like a pretty huge improvement to me. Why is this an abomination in your eyes?
> The original code was one giant unsafe block
True.
> has fewer bugs
Nope, this is demonstrably false because Rust has its own invariants around its types and the codebase is violating a lot of them.
> every potential memory issue is neatly annotated by an unsafe block
"Potential memory issue" can originate in unsafe blocks and safe code that are able to alternate the input condition of these unsafe blocks. Guess what? That still counts towards 100% in this code base, hence the abomination remark.
> refactor them out one by one
Not as easy as it sounds. They are like threads in a yarn ball, if there are one or two ends visible it's easier to sort them out. The actual situation is more like we have tens of thousands of ends (all the raw pointer code that comes with every shared object), to fix them it's basically a requirement to unwind the whole thing (rewrite all the callees and reorder the data flow as needed, redesigning all the APIs during that).
It's too early to declare it as anything remotely close to a win, optimistically saying.
> has fewer bugs
who claimed that? Are you suggesting that the rewrite did not introduce any new bugs? The correct answer is, by the way, that no one knows since it's millions of lines of code no one has properly read.
> smaller, faster
I thought this has already been debunked. You could just write better zig and make it smaller, faster (and have fewer bugs!)
given enough time and tokens, it will become that. I really don't understand how that is a problem in any way.
They’re just wildly successful terrible engineers who can describe problems well and have unlimited token budgets. If they were paying for their own token use, the software would be better, they simply don’t have financial incentive to be more performant.
A dirty secret of AI data centers are that they’re only getting 40-60% efficiency out of their GPU clusters and because the moneygun go brrrrr they just buy more.
You wonder why they’re so afraid of the Chinese competition… they can’t afford to be as wasteful
Incidentally, Claude Code has been very buggy for me lately (much more so than before). Lots of TUI rendering issues causing, e.g., the conversation history to be garbled etc.
I've been (grudgingly) using Claude since February.
When I started, I discovered to my shock that it was by far the worst TUI I had ever touched. Rendering glitches, keyboard input screwups, and just all-around jankiness.
Despite that awful baseline, I have to agree that it's gotten noticably worse in the past week or so.
It's started mangling my terminal sessions somehow, so that not all characters I input are visible in the UI.
Backgrounding it, doing a 'reset', then re-foregrounding seems to fix it.
Of course when I asked it to diagnose the problem, it assured me that Claude has no such big and it must be something else I'm running.
All I'm running is tmux and Claude, though, and the behavior surfaced while I was running Claude.
So, yeah - if they just recently updated Claude to use the Rust rewrite, this increased crappiness might actually be due to that. It does seem to at least roughly correlate.
Every time I resize my window now, the output is completely garbled. I often have to ask it to repeat itself just so I can see what it just said. This isn’t a new thing, but it feels like it’s gotten worse. This is on Windows
Same observation. One thing you can do is close out the session and `claude --resume`
Does exiting following by resuming the session fix it?
I'm far from being anti-AI, but these guys take it way too far IMO. It's straight-up AI slop. Like a real engineer still needs to be in the loop and drive the tool.
Anthropic seems to be all in on 100% AI code.
Ah so that's why it has been crashing constantly for me.
a terminal app now has a supply chain long enough to include a runtime acquisition. somewhere between "rewrote it in Rust" and "ship it" someone said "or we could just buy the company"
It’s interesting that Bun was a human rewrite from Go to Zig. (I think?). Then rewritten from Zig to Rust.
AI is pretty good at rewrites and ports. Quite good infact.
Whatever the headaches of the internals, I haven’t heard any substantive outcomes in hacker news that have been impacted by this change.
Yes if we had a Zig->Rust transpiler maybe it would produce similar output. But I can’t find one. We’d have to use an agent to build one first :)
Has all of this drama turned anyone else a bit sour on bun?
I have a long running side project I migrated to bun, and I'm starting to regret it. I don't want to build on top of this much churn.
Contrary to many, I have high hopes that Jarred and team will lapidate the ported codebase and it will continue to flourish as an open source project.
Damn, I should have not migrated to Bun. Should I revert back to Npm?
I am getting into the frontend dev and one thing that I don't understand is why people use bun in the first place? It's not much better preforming, it's not much safer, it's still not 100% compliant. Some tests show it's actually slower than node. Why bother switching, then?
I don’t think you would use Bun for front end.
Faster package manager
Faster startup
Typescript support out of the box
Better stdlib than node
Stdlib includes yaml, sqlite etc so you need to pull in fewer deps, so you can avoid the left-pad/is-even node_modules explosion problem to a greater extent
i assume it's because of all the built in tooling that node doesn't ship with.
There's always deno
but it's written in Rust too /s
What specific technical issues are you experiencing with running Bun that would justify a change?
What is the actual contribution and motivation of this post?
I don't blame him, if I had Anthropic's money hose pointed directly into my pocket I'd be spamming HN non-stop too
I've not made any money at all from Anthropic.
You can see my list of previous weekly blog sponsors here: https://simonwillison.net/dashboard/sponsor-history/
None of them get any influence on my content. That would hurt my credibility, and my credibility is the reason my site is worth sponsoring in the first place.
Honestly, if OpenAI or Anthropic offered to sponsor I'd probably turn them down. The optics of taking sponsorship from companies that I frequently write about are not great.
Fair, that rules out "Anthropic pays you directly."
But look at your own disclosure page [0]: OpenAI paid you for your time at a GPT-5 preview, and you regularly get early access, embargoed previews, and free API credits from OpenAI, Anthropic, Gemini, and Mistral. So "I've made no money from Anthropic" is narrower than it sounds, access and preferential treatment are compensation too, even if cash didn't directly change hands.
Same goes for the sponsor list. Microsoft is OpenAI's investor and infrastructure (or was anyways, I've got no clue what the status of that is these days), Amazon and Google are both major Anthropic investors, and most of that list runs on Azure, AWS, or GCP, or sells tools built on these labs' models. Taking a Microsoft sponsorship isn't really separate from an OpenAI one, it's just a single hop removed. The entire software ecosystem and all the players in it are entangled in this bubble.
I'm not accusing you of consciously hyping any of them. Your posts are high quality even when I disagree with the contents of them. You often list downsides too, prompt injection, security, slop issues but the throughline still repeats: this is inevitable, get on board. Product-market fit found, November 2025 as the inflection point. That kinda framing shows up again and again throughout all your posts.
It's refreshing that you're upfront about the previews and credits and all that jazz, but surely you understand why some people stay skeptical even with that disclosed as it confirms the access exists.
Whether you realize it or not, I think they are indeed paying you in some sense, which is part of why I'm skeptical when your posts consistently land at the top of HN. Not because the writing isn't good, but because I think the same incentive shaping the coverage probably shapes some of that reach too.
[0] https://simonwillison.net/about/#disclosures:~:text=2024%2E-...
Your comment here is fair, and it's why I take my disclosures seriously.
Nobody is unbiased, no matter how hard they might try. I like to get my information from sources where I understand their motivations, so my approach is to try to make my motivations as clear as possible.
(That's why I spend an unreasonable amount of energy arguing with people on Hacker News who call me a shill!)
People shouldn’t overthink blog posts. Just write what’s on your mind and have fun.
The motivation is obviously clear. No-one would be doing that for fun 24/7, only covering about AI and nothing else without getting paid for it.
If anyone else did that on HN, they would be accused of slop with their domain blacklisted.
"only covering AI" - don't miss my wildlife photography! https://simonwillison.net/elsewhere/sighting/
(Unless photos of actual pelicans count as "AI" content now.)
I just shipped this filter UI so you can see my other non-AI-tagged content in one place: https://simonwillison.net/search/?exclude.tag=ai
> "only covering AI" - don't miss my wildlife photography!
The "ai" tagged posts (2,100+) significantly outnumber "sighting" posts by orders of magnitude. Even searching HN, this post is the very first mention of it.
Perhaps that is why everyone here (except you) overlooks that or why we don't see much more of those sightings posts here either.
Yeah, wildlife photography is a new hobby - it used to be every few months, now it's several times a week.
I would be very surprised if one of my sightings posts made it to Hacker News. Maybe if I manage to snap a photo of an actual pelican perched on a bicycle some time.
There are many people with unbridled enthusiasm and an ability to write fast
Knowing Simon - he’s very much both :)
I thought it was interesting. I didn't write this with Hacker News in mind.
(I was actually half way through writing about something related, when I thought it would be interesting to see if I could prove that I had the Rust version of Bun on my laptop already.)
At this point we all know the answer
The port of Bun, which has >5000 open github issues, is used in Claude Code, which has >11000 open github issues. Do people use Bun in things that are expected to work reliably? Have any such projects tried the upgrade yet?
11k in two years vs 5k in two weeks? You're right, numbers speak for themself.
Did Bun mass-close issues that predated the rewrite? It doesn't look like they did, as the oldest open issue is from 2021 and there are many from 2022, but maybe they did something that killed most of the old issues.
Their (public) project management is horrible, you can find fixed issues unclosed and unfixed issues closed. Not really surprising when that part of the work is completely taken over by LLM agents though.
For real
I love bun - although disliked how Jarred did the conversion.
Project-wise, nothing has changed.
Bun was always great because of the fantastic dx - it was just really easy to use , with stuff like out of the box typescript (unreal that it took so long for node, and it's behind a super long flag, wtf...). And it didnt have the weirdness of deno, it maintained backwards compatability with node api, and it just worked.
But it was never stable. You'd have to be fool to believe that a single project could stably do everything bun covers. It's always been an insane project. It was built on top of zig, a langauge that hasn't reached 1.0, and is constantly changing, and throw in how he was rewriting his own custom zig stuff. Like c'mon, let's apply some common sense here.
For me, little has changed. I am still going to use bun as a nice dev tool, and use node for production.
Is it easier to rewrite Bun than it is to rewrite Claude?
Anthropic bought Bun, so they kinda, sorta had to make this work. I am sure the cost at $145,000 in Claude time will get some attention.
I am curious how this will work going forward from FOSS perspective. Will humans be allowed to modify the generated code? Only the .md prompts for the agents? Or what?
TIL about Bun.
Turns out it was just a build step after all.
So does that make Claude Code any better?
Can you select text with shift + arrow keys now in the command line client? :)
I despise this era we live in. Pushing rewrites like this upon millions of users, when the Bun rewrite has countless known issues and is likely a security nightmare. Every time I ‘brew outdated’ and I see a wall of updates I die a little inside knowing that most of this code has not been verified or even looked at. Yet we hear about massive supply chain attacks pretty much every week now and we’re still full steam ahead on this vibe coded nightmare. God help us. Claude Code in particular updates sometimes multiple times per day. Like I’m sorry but there is no way all this nonsense is safe.
pi runs in TypeScript and I like it, the target language of the tool, for me, matters only such that I can extend it. I like writing extensions, plugins, things, in TypeScript so I'm cool with that!
Claude Code is closed source, doesn't let me extend it beyond hooks, and these I write in bash anyways.
That all said, why should I bother about this change? Feels like a nothing burger to me, as an end user. This should matter more for those that are internal to Claude Code and Bun developing it.
Basically Anthropic can ship any trojan in underhanded Rust to any target because it is not possible to audit 1M lines of slop.
And the crowd is cheering.
It is absolutely amazing to me that this ai rewrite work so well, maybe claude is not really that much of a complicated tool to stress the bun runtime but still...
It works well because they had tests, they could compare before and after. Likelihood of issues especially if you transpile to a safer language should be minimal.
This post is just "they didn't lie"...
Yeah, I noticed. I had Claude write a quick JS script for me a few days ago, it then tried to use Bun to run it. When it couldn't find it, it tried to install it with `sudo pacman`. I had to fucking tell it to use Node instead.
as it always should've been Rust was the right move
bun upgrade --canary
you are welcome
Honestly, I initially thought rewriting an entire codebase with AI would be a huge mistake. After reading this, I'm starting to think I was wrong.
If projects like Bun can be substantially rewritten and shipped to millions of users, it suggests we're entering a very different phase of software development.
Today's AI-generated rewrites may not produce code that humans would consider high quality or maintainable. But I'm beginning to wonder whether that will even matter in a few months. If AI is the primary consumer, maintainer, and refactorer of code, human readability becomes far less important than correctness, performance, and the ability to iterate.
This feels like a shift where software may no longer exist as a long-lived artifact in its current form. Instead of writing and maintaining applications for years, we may generate, adapt, and discard them continuously for each use case.
> But I'm beginning to wonder whether that will even matter in a few months.
At that point, even Bun itself doesn't matter. All intermediate tools don't matter if LLMs can reliably write something large.
The problem is that LLM is not quite there yet. The rewrite was only possible because they mostly stick to 1-to-1 translation resulting in non-idiomatic Rust code. So, what from there? I don't think they can really build up a sane codebase from that state. They only shot themselves with a bigger gun.
> The rewrite was only possible because they mostly stick to 1-to-1 translation resulting in non-idiomatic Rust code.
That’s patently false, just read Jarred’s own blog post describing how that was the first stage only, they went through many more to get the amount of non idiomatic, unsafe Rust code to an acceptable level.
Somebody checked[1], and they discovered that the "stages" past the first had minimal impact on the unsafe blocks count. That's just one metric, but it makes me doubt your claim that there was/is a lot of work put into making the translated code idiomatic Rust.
[1] https://news.ycombinator.com/item?id=48967630
Isn't it just: "while true {refactorIdiomatically(); fixErrors()}"
/goal fix all bugs
That sounds like a massive waste of finite energy and compute resources.
That's like saying let's stay with horses.
We'll develop faster and better tech. We'll find resources to feed that. Use that to build better. Access better resources. We'll mine asteroids. We'll harness much more from the sun. The factory must grow.
Is that before or after the earths atmosphere acidifies for humans and our bodies can’t hold enough phosphorus or calcium for basic metabolic tasks? You have until 2050:
https://doi.org/10.1007/s11869-026-01918-5
We are the ones to get to decide. Do we want that? I don’t. But im just a single data point
> Honestly, I initially thought rewriting an entire codebase with AI would be a huge mistake. After reading this, I'm starting to think I was wrong.
> If projects like Bun can be substantially rewritten and shipped to millions of users, it suggests we're entering a very different phase of software development.
exactly. this wasn't a technical project. this was a marketing stunt that worked on you.
Seeing all the people up in arms that there was an automated rewrite of Bun to Rust has been very revealing and disappointing. Very silly behavior and denial over the inevitable.
> Startup got 10% faster on Linux but otherwise, barely anyone noticed.
Just that?
I was expecting more from that rewrite. Maybe Rust is not so worth it after all.
It was already written in a very performant language so no significant performance improvements should be expected.
The benefit of a rust rewrite is memory safety improvements, but currently they've just rewritten zig to unsafe rust so they don't have that either yet
The blog claims rust chosen mainly to address memory issues, which rust is a better language for. So, success would simply be less new memory errors / easier to patch old ones.
Claude installer/updater had a high memory usage problem (Gigabytes of resident memory used during a fresh installation of Clade with it's native install.sh script, or during a claude update). This was reported as early as December 2025, see https://github.com/anthropics/claude-code/issues/12327#issue....
The latest Claude installer (2.1.215) possibly does not have it anymore https://github.com/anthropics/claude-code/issues/4953#issuec..., but more tries on various machines are needed to confirm that.
I don't think their motivation was primarily user-visible stuff. They backed themselves into a corner by forking Zig, and also were fed up with fixing memory errors.
You wouldn't notice either of those if you were a user, unless you happened to hit one of those bugs.
I've been using Claude Code daily for a fairly large FastAPI project and didn't notice anything unusual around that timeframe. If this really was the Rust runtime underneath, "boring is good" seems like the right outcome.
Ok, so let me wrap this for everyone:
While everyone here in this forum kept arguing (and fighting and yelling at each other) whether tis moral/right/secure/cheap for ppl to rewrite and ship a major software package with LLMs/agents, one of the main drivers behind AI actually did it, without consulting your opinion, and most same everyone actually slurped this decision without paying a a notice.
Boring is good, but this boring is super massive major thing that happened, and precisely because security is still intact.
I have a better idea: convert it to a prompt and commit the prompt to the repository. Then Mythos will be your compiler.
the whole Ai skit is anthropomorphing the compiler as a coworker.
I'm looking at this situation strictly as 'What's possible today'. If a 1M lines code rewrite from one language to another goes into production in 1 month, that's a very strong signal that the models are now insanely capable.
My anxiety before merging a 2K lines PR is greatly reduced after 3 frontier models (Fable, 5.6 and kimi K3) finds no issues in it.
Just 6 months ago (Opus 4.6) this was not true, a big PR would have countless number of issues.
Aside from the human drama, the message to all of us is - these things are ready for whatever your imagination can throw at them.
I think that's exactly what Anthropic wanted to communicate.
It was not really a traditional rewrite. More like transpilation. Still impressive
> Aside from the human drama, the message to all of us is - these things are ready for whatever your imagination can throw at them.
…if you have the compute and capital to run that whole agentic system