Bun’s Rust rewrite shipped in Claude Code over a month ago and barely anyone noticed. Claude Code is widely used. The Rust rewrite is going well overall.
In the Bun v1.4 video, I promised a certain number of newly passing Node.js tests were added to force us to improve compatibility, and that number is not true yet. The release is delayed until it is true. The PRs to make it true are up but not merged yet. Most likely next Tuesday we’ll do the release of 1.4.
Take as long as you need to ensure software quality. A month without a release isn't a big deal and whomever needs a specific feature can offer to contribute or build themselves.
Node has 4-6 weeks without a meaningful release (other than security stuff) pretty much every December. I think the criticism in the article is unfounded and whomever needed/wanted a release should have asked first instead of writing an "angry" blog post.
Author here: I don't need or want another Bun release or an NPM release or anything like that. Like I very clearly say in the article I just got chatting with a peer about the Bun rewrite and I decided to take a look.
I'm consistently skeptical about new tech whether it is NoSQL or Blockchain or Serverless. Some of the things I'm skeptical about fail and some succeed.
Jarred, thank you for working on Bun. Many "vibe coded" :D projects start strong and are later abandoned (like potentially Anthropic C), so I understand why people worry about Bun's future. I hope Bun lasts for many years, like GCC. Bun is fast and great to use.
I don't see how it does. Claude Code is an extremely widely used product; the preceding comment offered an objective evaluation target, not a "trust me it's good" argument.
CI has always been expensive for Bun including before the acquisition. We build for [macOS, Linux, FreeBSD, Android, Windows] x [ARM64, x64] and then run tests on multiple Linux distros with multiple shards, multiple macOS versions and Windows for each architecture.
We recently started cross-compiling all the builds on Linux arm64 and that made it a little faster (I wrote a CLI tool to download the correct macOS headers for cross-compilation). We also have a daily cron job that asks claude to make the slowest tests faster while adding more assertions.
- How many people have updated Claude/Bun to the latest version.
- How many subscribers care about reporting issues. Most of them are forced to use the tool against their will and have mentally checked out already. Why report issues if your employer values slop code anyway. Just log the hours and keep your head down. Maybe it is not expedient for the AI narrative to report issues!
- How many subscriptions are real vs. bulk distiller accounts.
- If subscriber numbers are inflated.
Judging by the weird Claude Code Github issues page, there are suspiciously few new issues: about 2 to 3 a day only vs. alleged subscriber numbers of 4 million.
Either you mean retrospective, or you're being unnecessarily mean for something that's been getting quite a lot update reports, just on a social medium you probably don't use =P
I'm not sure how much insight we can glean from looking at the number of commits and release cadence here. In the aftermath of such a major refactor/rewrite, I would expect it to take some time to get back up to their usual development speed.
Jared and the other developers are new to the Rust codebase, even if the structure is largely familiar. They're also likely focusing on other priorities right now such as tracking down instances of 'unsafe', rather than making user-facing changes (which might encourage a release).
Bugfixes could encourage rapid new releases, but perhaps the rewrite simply hasn't been very buggy? As far as I know, those on the canary channel haven't reported any major issues, or even really noticed the change. So perhaps there's little reason for new releases right now, as the team slowly churns through the backlog.
> P.S. Anthropic’s C compiler and Cursor’s FastRender web browser haven’t had any commits for months.
I always assumed those were just experiments in capability, and weren't meant to be ongoing projects. I would hope that nobody is using them directly today.
Claude Code has a huge userbase. This is an impressive result so soon after the rewrite.
This is an impressive milestone for their rewrite. There are a lot of comments trying to downplay this as being unimpressive for some reason, but I can’t see them as anything other than sour grapes because the rewrite hasn’t crashed and burned like they were hoping.
If that is true, isn't it a bit unconventional? What version are they using, some random Git SHA? Why couldn't that have been made to a release or a release candidate at least?
The CI/CD costs are an interesting take, most of the rebuttals to AI ROI are something like “more code doesn’t mean more value!” but if you are charging per CI run then it actually does! Particularly with CI and extra testing being the main way to prevent the loops the AI companies are shilling from going off the rails
Author here: I'm also not sure how much we can glean from any of that!!! I look forward to Anthropic or Bun releasing a retrospective after their next release that fully outlines the cost.
Given their history with previous other marketing stunts I do not expect any retrospective. The technology is real but I have little faith in open and honest communication from Anthropic.
I've heard stories of LLMs changing tests to get all the tests to pass instead of actually fixing code. So I'm not sure I trust it just because tests pass. I also think that tests do not and cannot check everything.
I also don't trust it just because it compiles in Rust. The Rust compiler does not check everything.
So at what point do projects like this cross from "untrusted" to "trusted"?
I really do not understand how software developer think anymore. Using a LLM to translate a project in a short time, is by itself incredible. Just like one-shot whatever office clone.
But what makes software is not the fast creation of a "product" but that actual development of its features. Figuring out how everything needs to work together, fixing the bugs, and the o so boring UI work.
I have used LLMs to create stuff like word clones just for fun. It was a disaster. Sure, it had the basic functionality. But the moment you started with page structure (harder then one non-stop scrolling page), tables, images, rotating, and so many details that make up just the basics of word. Not even the extended functionality. You see every LLM just fall on its face.
Sure, i can clone sqlite from c to rust. Hell, i may even get it to do all the tests 100%. But there is a 99% chance that the clone will be slower, as it lacks the years of optimizations from the original language. There will be new bugs because of the language changeover. There is a need for future support and fixes.
People threat software like its something it is not. But unlike the past where your clients question your sanity for charging 100k for a piece of software. Not understanding its not just about writing the code. Now those expectation are even more pushed forwards, because of articles like this.
I constantly see software being published on reddit that does X, Y, Z only for the authors to abandon it as fast as they vibe coded it. Because fixing bugs is NOT sexy. Even with a LLM at your fingertips. Dealing with nagging users, is not sexy. Dealing with security issues, is NOT sexy. Dealing with data structure / databases, especially as your system changes ... you get the point.
Not understanding to the core the software you wrote, is going to exploded in your face.
This is why these stupid "we rewrote X into Z with a LLM in Y days" mean nothing. Its one thing to get a head start using this trick, its another to actually learn the code of your rewrite. And dedicated the time into maintaining the port, growing it, fixing it. This is where a lot of software fails. But now this crap is out there, instead of the maintained version of Zig, now we have a unmaintained Rust version that clouded the airwaves because if people now search for it, those articles "X in Z days" will pop up.
If you explore Github, you're gonna see thousands of abandoned game engines, compilers for made-up languages. And that has been happening since before the LLM era.
I used to be part of an OS messaging board in the early 2000s and almost everyone had their own OS. A dozen people or so could even run Firefox! I remember (now legend) Terry bothering us to check out LoseThos or GodOS or whatever was its name, but quite a few people had OSs that could do more than that.
Not all software needs to be commercial to be useful, even if it's just for a learning experience. I have learned a lot from those experiments, even if they're not polished.
> If you explore Github, you're gonna see thousands of abandoned game engines, compilers for made-up languages. And that has been happening since before the LLM era.
Yeah, but the people authoring those learned something.
> I used to be part of an OS messaging board in the early 2000s and almost everyone had their own OS.
Great example! I, too, once had my own toy OS, and browsed OSDev wiki nonstop. The thing is no one in the OS dev community were writing things they intended to place in front of actual users!
The difference now is that these incomplete projects:
a) Don't leave their owners any wiser than when they started, and
b) Are actually intended by their owners to be used by actual users.
> I have learned a lot from those experiments, even if they're not polished.
Would you have learned as much if you told a magic box "Make me an OS" and then slapped your name on it and uploaded it to GH?
> Not all software needs to be commercial to be useful, even if it's just for a learning experience. I have learned a lot from those experiments, even if they're not polished.
This is fine so long as the author is learning something (questionable) and not polluting the commons with "I made this in a weekend" vibe slop.
The more technical you get, the more subsitutable you become - or at least, people think of it in that way, because the whole idea is "It's not me, or the people, it's the raw technical prowess that earns its keep in this place".
But it seems like we're finally starting to accept that "accidentals" like network effects, ownership, accountability, etc. are important. Of course, that's why many of us fled to technical corners in the first place - because the "accidentals" become tied up with things like nepotism, unfair and arbitrary judges from random humans who don't understand your merit, the need for bullshitting more than real technical value. Supposedly, anyways.
My thoughts too. The LLMs made me understand that the world had been working like that long before LLMs. Luck plays an enormous part in life. We gravitated toward a discipline that seemed free of all those problems, when in fact it had those downfalls better disguised.
> Its one thing to get a head start using this trick, its another to actually learn the code of your rewrite.
I worked for a startup that stopped feature development and did a complete rewrite of a huge codebase. I was assigned to a side project during this time and missed the entire rewrite process. I came back to a completely rewritten codebase.
There was almost no learning curve, despite being in an entirely different language. The core architecture, data structures, and concepts were the same.
If you read the Bun blog post on how they did it, their rewrite was similar: The first step was getting it into a new language, not rearchitecting it from scratch.
I think they did it the right way based on my pre-LLM. Rewriting into a different language as fast and basically as possible is important for getting the team switched over quickly. Rewriting into a different language in X days is actually a good goal to minimize.
> There was almost no learning curve, despite being in an entirely different language. The core architecture, data structures, and concepts were the same.
> If you read the Bun blog post on how they did it, their rewrite was similar: The first step was getting it into a new language, not rearchitecting it from scratch
They eventually might regret this, when they are trying to get rid of the last lines of unsafe code. Rust needs to be written differently before you can write safe things to perform fast when compared to other languages or unsafe code. It takes a lot of experience before you can see it.
> I have used LLMs to create stuff like word clones just for fun. It was a disaster. Sure, it had the basic functionality. But the moment you started with page structure (harder then one non-stop scrolling page), tables, images, rotating, and so many details that make up just the basics of word. Not even the extended functionality. You see every LLM just fall on its face.
edit: Yeesh, misread your comment as "word games" not "word clones" and was very confused about the claim. Probably should have noted my confusion and re-read.
Are you comparing 2 relatively simple games with... Word?
Word is basically an operating system. Unix people like to make fun of Emacs for being one, but Word is basically one, too. And all the features in there are used, otherwise Microsoft wouldn't keep them around.
Nonsense. Provide/create proper tests for all features, and let the LLM test and fix everything.
In case of ccc (claudes C compiler) they just did not use any tests, though they are many existing C testsuite. They just stopped, when it finished compiling the kernel, still failing hundreds of tests.
Also I think porting code to another language or rewriting is one of the easier tasks for an LLM, since it has an extremely detailed spec (the source code itself) and a ton of tests already (hopefully).
In my experience, it will go to every length to convince you it has ported code that it hasn't. It will silently drop upstream unit tests it has no code for, if questioned it will insert some markdown giving some rational why that specific bit was deferred, after the fact, and then point you to it. This was Opus 4.6 for reference. I have had much better luck with small numbers of higher level tests that I can individually verify equivalency. I haven't tried having it do differential fuzzing on some high level interface, that seems like it might work in some cases. But to summarize, treat it like an adversary trying to deceive you.
It’s strange how you think AI is some static thing that only produces the type of output you experienced and isn’t constantly improving. My experience has proven the latter time and time again.
As a comparison point, someone decided to try to fix the issues in the Zig original and is now claiming sub-second build times, plus fixed bugs, by modernizing the codebase and sticking with best practices - indicating that all of the issues that justified the rewrite were self-inflicted and addressable.
I have no skin in this game, and the Zig version is also using LLMs if that helps take the culture war out of it. But, it has always been true in my experience that someone who really understands a problem space can outcompete someone who just throws resources (in hundreds of thousands of dollars of token spend) at it.
> indicating that all of the issues that justified the rewrite were self-inflicted and addressable
The main issue that justified the rewrite were memory bugs, especially related to interaction with GC managed Javascript objects. There is no fully general way to prevent those bugs in Zig, and I don't see any claims that they did so in Buz.
They also complained about build times, and in fact the Rust rewrite started immediately after some other drama about Bun being unable to contribute back LLM-written changes to the Zig compiler to improve build times, and the Zig team rejecting them in principle. So while memory issues did become the focus later, I don't think it was the entire story.
Migrating to Rust in a one-to-one translation with unsafe blocks does not make the code any more safe initially. It might provide tools to do a significant refactor that solves lifetime issues with Rust's help, but I haven't seen evidence that they've done that either. They're also embedding a large C++ codebase, JavaScriptCore, so there are always going to be unsafe areas and touchpoints where memory issues could live, and Rust won't magically solve them.
The bun rewrite inspired me to be much more aggressive on porting code, rewriting code, or vendoring external dependencies to tailor them specifically to our needs in ways that doesn’t make sense to upstream.
I feel like it made me generally more ambitious in what I’d throw at a coding model, but also made me focus a lot more on our testing harness and keeping a lot of it at the boundaries outside the language specific parts.
Having been part of several huge rewrites before, some multi-year long, I definitely would consider bun’s rewrite an enormous success. To keep such a level of test and feature parity, and add improvements on top of it, is a massive engineering feat.
I did suspect that the triumphalist pronouncements, and even the seemingly honest and forthright deep dive, were a little premature.
This is a key problem with LLM exuberance: it's very tempting to trade on decades of experience in software using LLMs, because one is tired of typing and manual figuring-out, it seems to work if you're competent, and the payoff is essentially immediate. The real bill comes in the mail much later.
I consider typing to be secondary to software engineering, but I do concede that for those cases that typing really is the bottleneck, LLMs can certainly be of value.
Oh, I 100% agree. I'm imagining the case where someone asks an LLM to do trivial things just for the novelty, or because they are fatigued of thinking + typing, but conceptualise the thing they are putting off as primarily a problem of typign and not thinking (I often do that).
I am fascinated by the discourse around this Bun rewrite. I read a lot of drama and personal accusations, there are pieces like this one trying to extract clues, and it seems everyone has a deeper ideological concern behind whatever they are trying to say. For this article, it seems to be skepticism towards AI and how successful it can be at replacing programmers. Other takes, like the one from the Zig maintainer, were also along those lines but more about the open source ethics and the future of that in a LLM world.
I am mostly bullish on AI capabilities, so from my perspective I don't see why we should be skeptical that frontier LLMs guided by experienced devs can translate whole libraries like that. Good follow-up questions would be how expensive it currently is to do so, and whether we will see people branching into all-in on AI versus no-AI camps as happened in this case.
You see this response because the port of Bun from Zig to Rust does not have anything to teach us about Zig, Rust or porting between languages with LLMs.
There are so many non-quantifiable properties to evaluate of the 'before' and 'after' codebases. Choices and preferences to be had about languages, language porting in general, and LLM coding.
After all that, pretend we could have a clear convincing distillation of the port and want to go apply the lessons learned. If someone doesn't get LLM porting results as good as Bun did, or it cost them substantially more in tokens, then they're "holding it wrong." If someone is underwhelmed by Bun's results, then it was just a proof of concept and the models have gotten so much better in the last 6 months anyway you can't compare.
I'm not sure Anthropic even cares about "releasing" the next version. The rust one has been in use in Claude Code for more than a month now, used by millions of people, and that's as far as they probably really worry about it. They bought Bun for Claude Code and I doubt the open source project matters to them otherwise.
If that is really what they are concerned with, they probably could have just had Claude Code rewrite Claude Code in rust? That likely would be far more efficient than changing the language of your typescript runtime that ships to run your react-based CLI app.
I imagine the $800k or whatever this has cost is coming out of Anthropic's marketing budget, so they can make a big splash about it.
> If that is really what they are concerned with, they probably could have just had Claude Code rewrite Claude Code in rust
Rewriting a runtime with well-defined interfaces and behavior is quite different from rewriting a user-facing application under active development by a decent chunk of their organization.
If you look at the reasons for rewriting Bun [0], they weren’t about efficiency and they don’t apply to Claude Code. It’s already written in a memory-safe language, and doesn’t have to interface to a library with a tricky set of invariants.
I very much doubt they would want to abandon the wider community. They do benefit from others using it.
To the contrary, I think any problem with this release would be jumped on harshly so they're being more careful than usual. There's not a rush for the community to move to 1.4 and any issues could poison the community trust.
It's just a marketing stunt. They've got the ad for Claude-powered code rewrites, and that worked beautifully. Everyone got the message: spend big bucks with Anthropic to get rid of whatever codebase bugs you - please, think of the IPO!
If it was about Claude Code itself, they could have rewritten it. They keep saying they don't even write code any more, so it shouldn't even matter what language it's in.
Everybody who has rewritten software understands the current phase: it mostly works, but there are always things to fix to make sure that there are no regressions, and the pressure is huge for any release.
I still believe it was the good decision, but I also know that I wouldn't be the first person to run the release in prod.
I think Jarred should start making release candidates instead of releases to take some of the pressure off.
This article could increase its credibility by being updated to acknowledge that Bun-on-Rust has been live in Claude Code itself since June 17th, and available as a canary release since it landed on main.
Rewrites of this scale certainly justify long canary release periods!
> Anthropic is dogfooding this, the machine is still ticking along, and Anthropic employees are directly involved.
The problem is that your article's central claim is that there hasn't been a Bun release since the Rust rewrite - which can be read as implying that the rewrite hasn't been used in production.
But it's been used in production on millions of machines running Claude Code for over a month!
I think failing to acknowledge that hurts the credibility of the article. It's been a heated discussion point in this thread already.
For me this is how all workflows with AI end up lookingif you really want robust products. Do whatever with AI, go fast (from the point of view of perception, initially) BUT it is not going to work without extra work.
and ho, the bloat, do not forget the bloat, which is technical debt towards the future.
I am not anti-ai per-se, but I consider the software I write as a prouct to add features to and maintain over time. So in this case I think it is not wise to say that bc you got something impressive fast you are done. Now you have bugs, architecture, bloat removal, and others...
Letting an AI manage all the workflow is a recipe for disaster in anything that is not strictly short-term. For this reason, I hardly code one-off scripts myself anymore and I hardly use AI for big things besides discussions with the prompt, reviews and snippets. For adding tests it can also be useful.
For full, long-term products, they try to sell agents, and tokens and the like. I think they do not work well enough what I tried. It always ends up as a bloated unmantainable mess.
Unless something that is totally autonomous (by this I mean 100% autonomous) and automated ever exists, I see writing software that can be maintained by humans still critical. As long as this exists, the productivity upper bound will be that of humans reviewing and driving the workflow, even if with AI support.
Many repeat the point of “$165k is cheaper than team of multiple engineers working on the rewrite for a year”, which I think is flawed — the team of engineers would have produced idiomatic rust, and it would take probably 100k+ of tokens more to make the bun in rust idiomatic rust.
This is assuming your engineers don't leave for higher-paying roles elsewhere. The market might be cold generally but for engineers working at these frontier AI companies it's red-hot.
And most executives are figuring this into their calculus right now because they were burned badly during COVID. Meta, Google, etc were loose with hiring and engineers flocked from their lower-paying companies in droves. The brain drain was real.
One public company I was at lost nearly 2/3rds of their engineers and mostly to Meta (granted, they had other problems but it was mostly about money -- the offers were excessive). Then market conditions forced them to freeze hiring and they've had a slow exodus of senior talent since as the firefighting has become constant.
AI adoption has only accelerated problems for them.
We've taken this "only two years and then leave" philosophy to an extreme and now companies are totally justified in not investing in their engineers anymore.
Would they have, in a year? The general plan of attack would likely still be the same: rewrite it in rust while keeping the structure as similar as possible, no matter how unidiomatic, then adjusting the design to make it more idiomatic to rust. Doing both at once is much harder.
IMO a team of engineers (presuming this is pre-AI) would have improved the existing Zig codebase, rather than spent time and money on a Rust port in the first place. In fact, I still think most teams of engineers would choose to improve what they have even now, circa AI.
Yes this is a typical case of showing results fast. I wonder what the cost for the remaining 10℅ of debugging and fixing all the bloat will be. Not so cheap I am guessing
Rust contains the ability to do everything that C can, if you use `unsafe`. And a file-by-file rewrite in Rust from another language usually involves keeping the ABI and API between files very C-like (and unsafe). In practice this means that the result of a first pass this way has all the memory safety of C code, but with worse readability because Rust makes unsafe things less ergonomic.
To actually get the safety benefits of Rust in a real way you have to rework those files to not treat eachother as C code. This is the interesting and the difficult part of a rewrite in Rust, and one that an unsupervised LLM rewrite is probably not even going to attempt.
I don't think this latter stage has actually happened with Bun's codebase. The result of the Rust rewrite in Bun's case is actually less safe than the Zig it is replacing, especially because (I am told) a lot of the new Rust code is unsound (introducing UB).
Presumably lots of stuff wrapped in 'unsafe'. I'm not a rust guy or a rust fan, and the last time I wrote something with Rust was like 7 years ago, but to my memory, because of how Rust manages mutability there are many access patterns that are Rust-specific; idiomatic Rust is going to use this patterns but they would be unlikely to show up in a language with a different type system / borrow checker / etc. etc.
This post doesn’t make sense. It was rewritten in Rust. The rewrite itself is complete (no more Zig).
Various people have claimed that Bun in Zig had a lot of tech debt. If they’re to be believed, it seems natural to assume the rewrite does, too. Perhaps all this activity is paying down some of that debt.
The author's assumption is that a rewrite is not just a mechanical translation of code - it's also a state of stability. And no release, for the author (I agree) means no stability.
It's like a developer who says that after a week of work, a feature is 90% ready, but the other 10% is still not ready (for release) after months.
Author kept "going" in title because there has been no minor/major release in last two months which unusual for this project if you review the older releases.
A major rewrite in another language is also unusual for this project.
It took TypeScript a year to go from announcing tsgo to releasing TypeScript 7.0. That work was done in parallel; here the work is being done serially — and it’s likely to take much less than a year for a new release.
bun in zig was used by many companies. some were using it in prod. how many of those are using it in prod? none, because bun in rust is not released yet.
Hence, the author concludes that rust rewrite is not complete as bun in rust is not released yet.
The rust version is being used by Claude Code though - which is a fairly large product!
I was hoping for more push back against https://bun.com/blog/bun-in-rust - which is pretty thorough and has some decent arguments and reasoning for why they did the rewrite.
> Various people have claimed that Bun in Zig had a lot of tech debt. If they’re to be believed,
This is one of the funnier takes on the rewrite. Bun was held up as a flagship Zig project for years. Then they chose to rewrite in Rust and everyone up to the Zig author has suddenly switched to claiming that Bun was terrible code all along.
If what they're claiming is true then what were they supposed to do? Go "Hey guys, it's the biggest project in Zig and it sucks, don't look at it"? Not exactly a good PR move.
tech dept is not a problem. to paraphrase captain Jack sparrow. "even if it were the most indepted working software project, IT WORKED".
On the other side of the medal we have a rewritten software that although it's trumpeted for it's rewrite speed, it is not showing the same Release speed as the manualy written, "tech dept ridden" old one.
Nope, they want shared artifact(s) between web and desktop (not sure what do they have in mobile apps) clients (Chat/Cowork/Code/CC-cli), so TS is the way to go. It’s a reasonable choice made by engineers.
I get that there's a baseline of unsafe that's necessary, but I was under the impression that some of those unsafes were in places where they could be replaced by more idiomatic Rust at a later date.
E.g. we should keep our wits about us when someone is making big hyperbolic claims about LLM that they directly benefit from, because maybe they have a motive to mislead either themselves, or us
I don't get it. Because they haven't cut a new arbitrary version number, we're denying it got done (in their perspective) and being used in a massive product already?
If you're being pedantic, no it's not "done," but nothing ever is.
It's not "done" if it's not stable and released. It's being canary tested by Claude Code users essentially but it's still being heavily worked on with tons of $ being poured into it and there's still no sign of them considering it stable and ready to go. That's the point of the article.
I'm gonna say it bluntly: I don't care about bun, never cared about bun and think nodejs is sufficient. The drama surrounding zig and rust still leaves me with a bad taste because I also don't like how nonsensical topics like that influence what we do and what we (have to) care about on a day to day basis. That is just my opinion!
Mechanisms of beliefs, sense of identity and pride are behind of majority of projects including opensource. These are the same mechanisms which produce what you call "drama".
We can't have commited and involved people working on opensource stuff and simultaneously avoid drama when their sence of identity/beliefs/pride is devalued.
I didn't follow the thing too closely when it happened. Sure, I was aware of the big picture. But wow, I didn't expect that after all this noise there still hasn't been a release? That's just crazy to me.
I shouldn't be surprised though, of course. Giving any credit or slack to a high-valuation LLM company is a silly endeavor.
Author here: An apology on the graphs, they just count rust files touched in commits, not total commits. So if there were two commits and one touched 3 .rs files and another touched 2, it'd be counted as 5 for the purposes of the graphs. I may fix this later but, yeah.
This doesn't answer the question posed in the title unfortunately. I am none the wiser about how it's going. The author just speculates that the rewrite isn't actually complete.
Coincidentally - I'm trying to get feedback on my own LLM rewrite project - MAME ROM machine code to Idiomatic JavaScript - the ability for an agent to understand blind code is remarkable.
Bun’s Rust rewrite shipped in Claude Code over a month ago and barely anyone noticed. Claude Code is widely used. The Rust rewrite is going well overall.
In the Bun v1.4 video, I promised a certain number of newly passing Node.js tests were added to force us to improve compatibility, and that number is not true yet. The release is delayed until it is true. The PRs to make it true are up but not merged yet. Most likely next Tuesday we’ll do the release of 1.4.
Take as long as you need to ensure software quality. A month without a release isn't a big deal and whomever needs a specific feature can offer to contribute or build themselves.
Node has 4-6 weeks without a meaningful release (other than security stuff) pretty much every December. I think the criticism in the article is unfounded and whomever needed/wanted a release should have asked first instead of writing an "angry" blog post.
(I'm a Node.js maintainer)
What is Node getting every 4-6 weeks that makes it noteworthy when it doesn't?
Author here: I don't need or want another Bun release or an NPM release or anything like that. Like I very clearly say in the article I just got chatting with a peer about the Bun rewrite and I decided to take a look.
I'm consistently skeptical about new tech whether it is NoSQL or Blockchain or Serverless. Some of the things I'm skeptical about fail and some succeed.
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Jarred, thank you for working on Bun. Many "vibe coded" :D projects start strong and are later abandoned (like potentially Anthropic C), so I understand why people worry about Bun's future. I hope Bun lasts for many years, like GCC. Bun is fast and great to use.
Anthropic's C compiler was a proof of concept[1], so it makes sense that it was abandoned.
[1] What it actually proved is up for debate.
In Dutch there's a saying, "wij van wc eend adviseren wc eend", and it fits perfectly.
I don't see how it does. Claude Code is an extremely widely used product; the preceding comment offered an objective evaluation target, not a "trust me it's good" argument.
Frenchman here, I Google Translated that and it says
"We at WC Duck recommend WC Duck"... I'm left scratching my head, if you'd care to spell out what the saying means for non-Dutch I'd appreciate it :)
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Any comment on the costs estimated in the article? especially the buildkite costs?
CI has always been expensive for Bun including before the acquisition. We build for [macOS, Linux, FreeBSD, Android, Windows] x [ARM64, x64] and then run tests on multiple Linux distros with multiple shards, multiple macOS versions and Windows for each architecture.
We recently started cross-compiling all the builds on Linux arm64 and that made it a little faster (I wrote a CLI tool to download the correct macOS headers for cross-compilation). We also have a daily cron job that asks claude to make the slowest tests faster while adding more assertions.
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We would need to know at least:
- How many people have updated Claude/Bun to the latest version.
- How many subscribers care about reporting issues. Most of them are forced to use the tool against their will and have mentally checked out already. Why report issues if your employer values slop code anyway. Just log the hours and keep your head down. Maybe it is not expedient for the AI narrative to report issues!
- How many subscriptions are real vs. bulk distiller accounts.
- If subscriber numbers are inflated.
Judging by the weird Claude Code Github issues page, there are suspiciously few new issues: about 2 to 3 a day only vs. alleged subscriber numbers of 4 million.
> How many people have updated Claude/Bun to the latest version
By default, Claude Code updates itself all the time without asking for permission, so I'd say most users are on the latest versions.
Any chance for 1.3.15 with bugfixes for the rest of us?
Yeah, 1.3.14 has some bad regressions. 1.3.11 is ideal for tests CI. Or canary. For production, I don’t have any advice. There will be no 1.3.15.
> The Rust rewrite is going well overall.
I look forward to the postmortem!
https://bun.com/blog/bun-in-rust
This is from July 8, 2026. And while you did link it in your article, what else are you expecting?
Either you mean retrospective, or you're being unnecessarily mean for something that's been getting quite a lot update reports, just on a social medium you probably don't use =P
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I'm not sure how much insight we can glean from looking at the number of commits and release cadence here. In the aftermath of such a major refactor/rewrite, I would expect it to take some time to get back up to their usual development speed.
Jared and the other developers are new to the Rust codebase, even if the structure is largely familiar. They're also likely focusing on other priorities right now such as tracking down instances of 'unsafe', rather than making user-facing changes (which might encourage a release).
Bugfixes could encourage rapid new releases, but perhaps the rewrite simply hasn't been very buggy? As far as I know, those on the canary channel haven't reported any major issues, or even really noticed the change. So perhaps there's little reason for new releases right now, as the team slowly churns through the backlog.
> P.S. Anthropic’s C compiler and Cursor’s FastRender web browser haven’t had any commits for months.
I always assumed those were just experiments in capability, and weren't meant to be ongoing projects. I would hope that nobody is using them directly today.
They also have made a release, in a sense, since they moved all Claude code users to it a month ago. (And apparently no one noticed).
I think they're taking things "gradually" as they are under a lot of scrutiny and no rush for full release.
Claude Code has a huge userbase. This is an impressive result so soon after the rewrite.
This is an impressive milestone for their rewrite. There are a lot of comments trying to downplay this as being unimpressive for some reason, but I can’t see them as anything other than sour grapes because the rewrite hasn’t crashed and burned like they were hoping.
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If that is true, isn't it a bit unconventional? What version are they using, some random Git SHA? Why couldn't that have been made to a release or a release candidate at least?
I've had several bun-related crashes in Claude code in the last week, which I don't remember ever seeing before then.
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Claude Code most likely only uses a tiny fraction of Bun/Node features, so Claude Code switching to the Rust rewrite doesn't mean all that much.
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The CI/CD costs are an interesting take, most of the rebuttals to AI ROI are something like “more code doesn’t mean more value!” but if you are charging per CI run then it actually does! Particularly with CI and extra testing being the main way to prevent the loops the AI companies are shilling from going off the rails
Author here: I'm also not sure how much we can glean from any of that!!! I look forward to Anthropic or Bun releasing a retrospective after their next release that fully outlines the cost.
Given their history with previous other marketing stunts I do not expect any retrospective. The technology is real but I have little faith in open and honest communication from Anthropic.
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There is no incentive for them to be honest about the downsides and problems.
At what point should I trust projects like this?
I've heard stories of LLMs changing tests to get all the tests to pass instead of actually fixing code. So I'm not sure I trust it just because tests pass. I also think that tests do not and cannot check everything.
I also don't trust it just because it compiles in Rust. The Rust compiler does not check everything.
So at what point do projects like this cross from "untrusted" to "trusted"?
I really do not understand how software developer think anymore. Using a LLM to translate a project in a short time, is by itself incredible. Just like one-shot whatever office clone.
But what makes software is not the fast creation of a "product" but that actual development of its features. Figuring out how everything needs to work together, fixing the bugs, and the o so boring UI work.
I have used LLMs to create stuff like word clones just for fun. It was a disaster. Sure, it had the basic functionality. But the moment you started with page structure (harder then one non-stop scrolling page), tables, images, rotating, and so many details that make up just the basics of word. Not even the extended functionality. You see every LLM just fall on its face.
Sure, i can clone sqlite from c to rust. Hell, i may even get it to do all the tests 100%. But there is a 99% chance that the clone will be slower, as it lacks the years of optimizations from the original language. There will be new bugs because of the language changeover. There is a need for future support and fixes.
People threat software like its something it is not. But unlike the past where your clients question your sanity for charging 100k for a piece of software. Not understanding its not just about writing the code. Now those expectation are even more pushed forwards, because of articles like this.
I constantly see software being published on reddit that does X, Y, Z only for the authors to abandon it as fast as they vibe coded it. Because fixing bugs is NOT sexy. Even with a LLM at your fingertips. Dealing with nagging users, is not sexy. Dealing with security issues, is NOT sexy. Dealing with data structure / databases, especially as your system changes ... you get the point.
Not understanding to the core the software you wrote, is going to exploded in your face.
This is why these stupid "we rewrote X into Z with a LLM in Y days" mean nothing. Its one thing to get a head start using this trick, its another to actually learn the code of your rewrite. And dedicated the time into maintaining the port, growing it, fixing it. This is where a lot of software fails. But now this crap is out there, instead of the maintained version of Zig, now we have a unmaintained Rust version that clouded the airwaves because if people now search for it, those articles "X in Z days" will pop up.
What have we become ...
I think this is perfectly fine.
If you explore Github, you're gonna see thousands of abandoned game engines, compilers for made-up languages. And that has been happening since before the LLM era.
I used to be part of an OS messaging board in the early 2000s and almost everyone had their own OS. A dozen people or so could even run Firefox! I remember (now legend) Terry bothering us to check out LoseThos or GodOS or whatever was its name, but quite a few people had OSs that could do more than that.
Not all software needs to be commercial to be useful, even if it's just for a learning experience. I have learned a lot from those experiments, even if they're not polished.
> If you explore Github, you're gonna see thousands of abandoned game engines, compilers for made-up languages. And that has been happening since before the LLM era.
Yeah, but the people authoring those learned something.
> I used to be part of an OS messaging board in the early 2000s and almost everyone had their own OS.
Great example! I, too, once had my own toy OS, and browsed OSDev wiki nonstop. The thing is no one in the OS dev community were writing things they intended to place in front of actual users!
The difference now is that these incomplete projects:
a) Don't leave their owners any wiser than when they started, and
b) Are actually intended by their owners to be used by actual users.
> I have learned a lot from those experiments, even if they're not polished.
Would you have learned as much if you told a magic box "Make me an OS" and then slapped your name on it and uploaded it to GH?
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> (now legend) Terry bothering us to check out LoseThos or GodOS or whatever was its name
Temple OS :)
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> Not all software needs to be commercial to be useful, even if it's just for a learning experience. I have learned a lot from those experiments, even if they're not polished.
This is fine so long as the author is learning something (questionable) and not polluting the commons with "I made this in a weekend" vibe slop.
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LoseThOS didn't burn through hundreds of thousands of dollars of expensive and environmentally questionable compute.
The more technical you get, the more subsitutable you become - or at least, people think of it in that way, because the whole idea is "It's not me, or the people, it's the raw technical prowess that earns its keep in this place".
But it seems like we're finally starting to accept that "accidentals" like network effects, ownership, accountability, etc. are important. Of course, that's why many of us fled to technical corners in the first place - because the "accidentals" become tied up with things like nepotism, unfair and arbitrary judges from random humans who don't understand your merit, the need for bullshitting more than real technical value. Supposedly, anyways.
My thoughts too. The LLMs made me understand that the world had been working like that long before LLMs. Luck plays an enormous part in life. We gravitated toward a discipline that seemed free of all those problems, when in fact it had those downfalls better disguised.
I think it is a very good point: "because the "accidentals" become tied up with things like nepotism, unfair and arbitrary"
I never thought of this from this perspective but indeed it seems to be totally true.
> Its one thing to get a head start using this trick, its another to actually learn the code of your rewrite.
I worked for a startup that stopped feature development and did a complete rewrite of a huge codebase. I was assigned to a side project during this time and missed the entire rewrite process. I came back to a completely rewritten codebase.
There was almost no learning curve, despite being in an entirely different language. The core architecture, data structures, and concepts were the same.
If you read the Bun blog post on how they did it, their rewrite was similar: The first step was getting it into a new language, not rearchitecting it from scratch.
I think they did it the right way based on my pre-LLM. Rewriting into a different language as fast and basically as possible is important for getting the team switched over quickly. Rewriting into a different language in X days is actually a good goal to minimize.
> There was almost no learning curve, despite being in an entirely different language. The core architecture, data structures, and concepts were the same.
> If you read the Bun blog post on how they did it, their rewrite was similar: The first step was getting it into a new language, not rearchitecting it from scratch
They eventually might regret this, when they are trying to get rid of the last lines of unsafe code. Rust needs to be written differently before you can write safe things to perform fast when compared to other languages or unsafe code. It takes a lot of experience before you can see it.
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> Not understanding to the core the software you wrote, is going to exploded in your face.
Short-termism at its peak. Code maintainers will learn the hard way how to set the boundaries between ai-generated code, and human maintainable code.
> I constantly see software being published on reddit that does X, Y, Z only for the authors to abandon it as fast as they vibe coded it.
Also if you whip something up, you tend not to care for it as much as something you took the time to create in a "proper" manner.
> I have used LLMs to create stuff like word clones just for fun. It was a disaster. Sure, it had the basic functionality. But the moment you started with page structure (harder then one non-stop scrolling page), tables, images, rotating, and so many details that make up just the basics of word. Not even the extended functionality. You see every LLM just fall on its face.
What do you think of https://scramblequest.app and https://wordpeek.app ?
I have never looked at any of the code for them
edit: Yeesh, misread your comment as "word games" not "word clones" and was very confused about the claim. Probably should have noted my confusion and re-read.
I think they might mean Word as in Microsoft Word. Just based on the feature list they were describing.
Are you comparing 2 relatively simple games with... Word?
Word is basically an operating system. Unix people like to make fun of Emacs for being one, but Word is basically one, too. And all the features in there are used, otherwise Microsoft wouldn't keep them around.
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Nonsense. Provide/create proper tests for all features, and let the LLM test and fix everything.
In case of ccc (claudes C compiler) they just did not use any tests, though they are many existing C testsuite. They just stopped, when it finished compiling the kernel, still failing hundreds of tests.
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Also I think porting code to another language or rewriting is one of the easier tasks for an LLM, since it has an extremely detailed spec (the source code itself) and a ton of tests already (hopefully).
In my experience, it will go to every length to convince you it has ported code that it hasn't. It will silently drop upstream unit tests it has no code for, if questioned it will insert some markdown giving some rational why that specific bit was deferred, after the fact, and then point you to it. This was Opus 4.6 for reference. I have had much better luck with small numbers of higher level tests that I can individually verify equivalency. I haven't tried having it do differential fuzzing on some high level interface, that seems like it might work in some cases. But to summarize, treat it like an adversary trying to deceive you.
It’s strange how you think AI is some static thing that only produces the type of output you experienced and isn’t constantly improving. My experience has proven the latter time and time again.
> Using a LLM to translate a project in a short time, is by itself incredible.
Not really. Transpilers have existed since forever.
The hard part is all the edge cases. (And LLMs don't solve this problem; they probably akshually exacerbate it.)
As a comparison point, someone decided to try to fix the issues in the Zig original and is now claiming sub-second build times, plus fixed bugs, by modernizing the codebase and sticking with best practices - indicating that all of the issues that justified the rewrite were self-inflicted and addressable.
https://ziggit.dev/t/buz-a-drop-in-replacement-for-bun-using...
I have no skin in this game, and the Zig version is also using LLMs if that helps take the culture war out of it. But, it has always been true in my experience that someone who really understands a problem space can outcompete someone who just throws resources (in hundreds of thousands of dollars of token spend) at it.
> indicating that all of the issues that justified the rewrite were self-inflicted and addressable
The main issue that justified the rewrite were memory bugs, especially related to interaction with GC managed Javascript objects. There is no fully general way to prevent those bugs in Zig, and I don't see any claims that they did so in Buz.
They also complained about build times, and in fact the Rust rewrite started immediately after some other drama about Bun being unable to contribute back LLM-written changes to the Zig compiler to improve build times, and the Zig team rejecting them in principle. So while memory issues did become the focus later, I don't think it was the entire story.
Migrating to Rust in a one-to-one translation with unsafe blocks does not make the code any more safe initially. It might provide tools to do a significant refactor that solves lifetime issues with Rust's help, but I haven't seen evidence that they've done that either. They're also embedding a large C++ codebase, JavaScriptCore, so there are always going to be unsafe areas and touchpoints where memory issues could live, and Rust won't magically solve them.
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The bun rewrite inspired me to be much more aggressive on porting code, rewriting code, or vendoring external dependencies to tailor them specifically to our needs in ways that doesn’t make sense to upstream.
I feel like it made me generally more ambitious in what I’d throw at a coding model, but also made me focus a lot more on our testing harness and keeping a lot of it at the boundaries outside the language specific parts.
Having been part of several huge rewrites before, some multi-year long, I definitely would consider bun’s rewrite an enormous success. To keep such a level of test and feature parity, and add improvements on top of it, is a massive engineering feat.
I did suspect that the triumphalist pronouncements, and even the seemingly honest and forthright deep dive, were a little premature.
This is a key problem with LLM exuberance: it's very tempting to trade on decades of experience in software using LLMs, because one is tired of typing and manual figuring-out, it seems to work if you're competent, and the payoff is essentially immediate. The real bill comes in the mail much later.
>because one is tired of typing
I consider typing to be secondary to software engineering, but I do concede that for those cases that typing really is the bottleneck, LLMs can certainly be of value.
Those cases are rare, though.
Oh, I 100% agree. I'm imagining the case where someone asks an LLM to do trivial things just for the novelty, or because they are fatigued of thinking + typing, but conceptualise the thing they are putting off as primarily a problem of typign and not thinking (I often do that).
I am fascinated by the discourse around this Bun rewrite. I read a lot of drama and personal accusations, there are pieces like this one trying to extract clues, and it seems everyone has a deeper ideological concern behind whatever they are trying to say. For this article, it seems to be skepticism towards AI and how successful it can be at replacing programmers. Other takes, like the one from the Zig maintainer, were also along those lines but more about the open source ethics and the future of that in a LLM world.
I am mostly bullish on AI capabilities, so from my perspective I don't see why we should be skeptical that frontier LLMs guided by experienced devs can translate whole libraries like that. Good follow-up questions would be how expensive it currently is to do so, and whether we will see people branching into all-in on AI versus no-AI camps as happened in this case.
> experienced devs
No one on their team had Rust experience
You see this response because the port of Bun from Zig to Rust does not have anything to teach us about Zig, Rust or porting between languages with LLMs.
There are so many non-quantifiable properties to evaluate of the 'before' and 'after' codebases. Choices and preferences to be had about languages, language porting in general, and LLM coding.
After all that, pretend we could have a clear convincing distillation of the port and want to go apply the lessons learned. If someone doesn't get LLM porting results as good as Bun did, or it cost them substantially more in tokens, then they're "holding it wrong." If someone is underwhelmed by Bun's results, then it was just a proof of concept and the models have gotten so much better in the last 6 months anyway you can't compare.
I'm not sure Anthropic even cares about "releasing" the next version. The rust one has been in use in Claude Code for more than a month now, used by millions of people, and that's as far as they probably really worry about it. They bought Bun for Claude Code and I doubt the open source project matters to them otherwise.
If that is really what they are concerned with, they probably could have just had Claude Code rewrite Claude Code in rust? That likely would be far more efficient than changing the language of your typescript runtime that ships to run your react-based CLI app.
I imagine the $800k or whatever this has cost is coming out of Anthropic's marketing budget, so they can make a big splash about it.
> If that is really what they are concerned with, they probably could have just had Claude Code rewrite Claude Code in rust
Rewriting a runtime with well-defined interfaces and behavior is quite different from rewriting a user-facing application under active development by a decent chunk of their organization.
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If you look at the reasons for rewriting Bun [0], they weren’t about efficiency and they don’t apply to Claude Code. It’s already written in a memory-safe language, and doesn’t have to interface to a library with a tricky set of invariants.
[0] https://bun.com/blog/bun-in-rust
I very much doubt they would want to abandon the wider community. They do benefit from others using it.
To the contrary, I think any problem with this release would be jumped on harshly so they're being more careful than usual. There's not a rush for the community to move to 1.4 and any issues could poison the community trust.
Like this rewrite did not terminally poison trust?
Why wouldn't they?
Bun is a major part of the web ecosystem, having it developed by them via AI, sounds like a gigantic pr win.
Anyone know why? Can’t CC run on any JS runtime?
Yes, but it’s slower on non-bun runtimes. Nowadays, I believe they bundle bun with CC
They chose to use a react rendering to native TUI renderer, which was a source of a lot of performance issues.
AFAIK, they have written a new renderer.
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because their js code is so bad and slow that they need the bun performance hacks and optimisations.
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It's just a marketing stunt. They've got the ad for Claude-powered code rewrites, and that worked beautifully. Everyone got the message: spend big bucks with Anthropic to get rid of whatever codebase bugs you - please, think of the IPO!
If it was about Claude Code itself, they could have rewritten it. They keep saying they don't even write code any more, so it shouldn't even matter what language it's in.
Everybody who has rewritten software understands the current phase: it mostly works, but there are always things to fix to make sure that there are no regressions, and the pressure is huge for any release.
I still believe it was the good decision, but I also know that I wouldn't be the first person to run the release in prod.
I think Jarred should start making release candidates instead of releases to take some of the pressure off.
This article could increase its credibility by being updated to acknowledge that Bun-on-Rust has been live in Claude Code itself since June 17th, and available as a canary release since it landed on main.
Rewrites of this scale certainly justify long canary release periods!
I mention Anthropic dogfooding this in the article.
In this sentence, sure:
> Anthropic is dogfooding this, the machine is still ticking along, and Anthropic employees are directly involved.
The problem is that your article's central claim is that there hasn't been a Bun release since the Rust rewrite - which can be read as implying that the rewrite hasn't been used in production.
But it's been used in production on millions of machines running Claude Code for over a month!
I think failing to acknowledge that hurts the credibility of the article. It's been a heated discussion point in this thread already.
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Just a couple more 100hr weeks of debugging, and the last 80% will be done :-)
For me this is how all workflows with AI end up lookingif you really want robust products. Do whatever with AI, go fast (from the point of view of perception, initially) BUT it is not going to work without extra work.
and ho, the bloat, do not forget the bloat, which is technical debt towards the future.
I am not anti-ai per-se, but I consider the software I write as a prouct to add features to and maintain over time. So in this case I think it is not wise to say that bc you got something impressive fast you are done. Now you have bugs, architecture, bloat removal, and others...
Letting an AI manage all the workflow is a recipe for disaster in anything that is not strictly short-term. For this reason, I hardly code one-off scripts myself anymore and I hardly use AI for big things besides discussions with the prompt, reviews and snippets. For adding tests it can also be useful.
For full, long-term products, they try to sell agents, and tokens and the like. I think they do not work well enough what I tried. It always ends up as a bloated unmantainable mess.
Unless something that is totally autonomous (by this I mean 100% autonomous) and automated ever exists, I see writing software that can be maintained by humans still critical. As long as this exists, the productivity upper bound will be that of humans reviewing and driving the workflow, even if with AI support.
Many repeat the point of “$165k is cheaper than team of multiple engineers working on the rewrite for a year”, which I think is flawed — the team of engineers would have produced idiomatic rust, and it would take probably 100k+ of tokens more to make the bun in rust idiomatic rust.
They also would have produced a team of engineers that knows the Rust codebase.
"Knowing the codebase" seems like an antithetical philosophy to LLM driven engineering orgs.
This is assuming your engineers don't leave for higher-paying roles elsewhere. The market might be cold generally but for engineers working at these frontier AI companies it's red-hot.
And most executives are figuring this into their calculus right now because they were burned badly during COVID. Meta, Google, etc were loose with hiring and engineers flocked from their lower-paying companies in droves. The brain drain was real.
One public company I was at lost nearly 2/3rds of their engineers and mostly to Meta (granted, they had other problems but it was mostly about money -- the offers were excessive). Then market conditions forced them to freeze hiring and they've had a slow exodus of senior talent since as the firefighting has become constant.
AI adoption has only accelerated problems for them.
We've taken this "only two years and then leave" philosophy to an extreme and now companies are totally justified in not investing in their engineers anymore.
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I feel your estimate of tokens is a few orders of magnitude off, it’s on the low side.
I use more (albeit cached) when centering a div.
I think they missed a $ sign, i.e. they meant $100k of tokens
This is where we've come to where people proudly proclaim using an AI to do what is a single line of CSS.
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100k tokens is your pre-prompt and your CLAUDE.md as well as a few files from your root.
What a great joke.
I will have to steal it for an upcoming AI tools meeting I have at work.
Also, pretty clever as centering a div w/ CSS has been notoriously difficult to achieve.
Would they have, in a year? The general plan of attack would likely still be the same: rewrite it in rust while keeping the structure as similar as possible, no matter how unidiomatic, then adjusting the design to make it more idiomatic to rust. Doing both at once is much harder.
IMO a team of engineers (presuming this is pre-AI) would have improved the existing Zig codebase, rather than spent time and money on a Rust port in the first place. In fact, I still think most teams of engineers would choose to improve what they have even now, circa AI.
I doubt file by file rewriting takes as much work as rewriting and refactoring the code - especially at this scale.
Yes this is a typical case of showing results fast. I wonder what the cost for the remaining 10℅ of debugging and fixing all the bloat will be. Not so cheap I am guessing
> produced idiomatic rust
I keep seeing this. What is "un-idiomatic" rust?
Rust contains the ability to do everything that C can, if you use `unsafe`. And a file-by-file rewrite in Rust from another language usually involves keeping the ABI and API between files very C-like (and unsafe). In practice this means that the result of a first pass this way has all the memory safety of C code, but with worse readability because Rust makes unsafe things less ergonomic.
To actually get the safety benefits of Rust in a real way you have to rework those files to not treat eachother as C code. This is the interesting and the difficult part of a rewrite in Rust, and one that an unsupervised LLM rewrite is probably not even going to attempt.
I don't think this latter stage has actually happened with Bun's codebase. The result of the Rust rewrite in Bun's case is actually less safe than the Zig it is replacing, especially because (I am told) a lot of the new Rust code is unsound (introducing UB).
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Presumably lots of stuff wrapped in 'unsafe'. I'm not a rust guy or a rust fan, and the last time I wrote something with Rust was like 7 years ago, but to my memory, because of how Rust manages mutability there are many access patterns that are Rust-specific; idiomatic Rust is going to use this patterns but they would be unlikely to show up in a language with a different type system / borrow checker / etc. etc.
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> I hadn’t seen the numbers for the CI/CD costs of Buildkite, and as you might have noticed from above, some PRs were written by Anthropic employees.
The leaked code of the claude had switch flag where claude pretends to be employee. You can't trust/expect that those PR's were authored by people.
> some PRs were written by Anthropic employees
Oh, that company that I heard did not use humans aymore to write software and bragged about it? I heard, correct me if I am wrong.
Something does not match here...
This post doesn’t make sense. It was rewritten in Rust. The rewrite itself is complete (no more Zig).
Various people have claimed that Bun in Zig had a lot of tech debt. If they’re to be believed, it seems natural to assume the rewrite does, too. Perhaps all this activity is paying down some of that debt.
> This post doesn’t make sense
The author's assumption is that a rewrite is not just a mechanical translation of code - it's also a state of stability. And no release, for the author (I agree) means no stability.
It's like a developer who says that after a week of work, a feature is 90% ready, but the other 10% is still not ready (for release) after months.
Author kept "going" in title because there has been no minor/major release in last two months which unusual for this project if you review the older releases.
A major rewrite in another language is also unusual for this project.
It took TypeScript a year to go from announcing tsgo to releasing TypeScript 7.0. That work was done in parallel; here the work is being done serially — and it’s likely to take much less than a year for a new release.
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bun in zig was used by many companies. some were using it in prod. how many of those are using it in prod? none, because bun in rust is not released yet.
Hence, the author concludes that rust rewrite is not complete as bun in rust is not released yet.
I agree with author's POV.
The rust version is being used by Claude Code though - which is a fairly large product!
I was hoping for more push back against https://bun.com/blog/bun-in-rust - which is pretty thorough and has some decent arguments and reasoning for why they did the rewrite.
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> Various people have claimed that Bun in Zig had a lot of tech debt. If they’re to be believed,
This is one of the funnier takes on the rewrite. Bun was held up as a flagship Zig project for years. Then they chose to rewrite in Rust and everyone up to the Zig author has suddenly switched to claiming that Bun was terrible code all along.
If what they're claiming is true then what were they supposed to do? Go "Hey guys, it's the biggest project in Zig and it sucks, don't look at it"? Not exactly a good PR move.
> Perhaps all this activity is paying down some of that debt.
Perhaps. But were that the case, one would think they'd be quite eager to say so.
Maybe they will!
Are you expecting them to live-tweet their work or something?
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tech dept is not a problem. to paraphrase captain Jack sparrow. "even if it were the most indepted working software project, IT WORKED". On the other side of the medal we have a rewritten software that although it's trumpeted for it's rewrite speed, it is not showing the same Release speed as the manualy written, "tech dept ridden" old one.
Why did they buy an open source project anyway? If is not “officially” supported why not fork and use? Claude code is probably the most used anyway
They bought the maintainers, not the code.
Why though? Isn't AI supposed to take care of such things?
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To me it just looks like a marketing stunt.
Maybe it would have made more sense for Anthropic to rewrite Claude Code in rust, and cut out the middle man (bun)?
Nope, they want shared artifact(s) between web and desktop (not sure what do they have in mobile apps) clients (Chat/Cowork/Code/CC-cli), so TS is the way to go. It’s a reasonable choice made by engineers.
Pretty sure rust can run on browsers;
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One metric I thought might be interesting with respect to the Rust rewrite is the number of "unsafe" occurrences in the code.
I was optimistic those would be going down over time but it looks like they've stayed pretty constant: https://news.ycombinator.com/item?id=48966569#48967630
Does that data exclude FFI wrappers, which necessarily must be unsafe? If not, don’t put much stock in it.
No, it's a raw count.
I get that there's a baseline of unsafe that's necessary, but I was under the impression that some of those unsafes were in places where they could be replaced by more idiomatic Rust at a later date.
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> _"...Canny..."_
What a time to be alive
Came to point this out as well. Very bizarre that it was capitalized. Italics or bold might even have been acceptable...
Yeah, I noticed that too and kept wondering who this Canny was that the author wants to be? Felt a bit un-Canny...
More proof that it was written by a human!!!
Still have no idea what that means…
https://www.merriam-webster.com/dictionary/canny
It means shrewd.
E.g. we should keep our wits about us when someone is making big hyperbolic claims about LLM that they directly benefit from, because maybe they have a motive to mislead either themselves, or us
I don't get it. Because they haven't cut a new arbitrary version number, we're denying it got done (in their perspective) and being used in a massive product already?
If you're being pedantic, no it's not "done," but nothing ever is.
It's not "done" if it's not stable and released. It's being canary tested by Claude Code users essentially but it's still being heavily worked on with tons of $ being poured into it and there's still no sign of them considering it stable and ready to go. That's the point of the article.
> and being used in a massive product already?
One single product, AFAIK, and one ladden with bugs and issue too.
I'm gonna say it bluntly: I don't care about bun, never cared about bun and think nodejs is sufficient. The drama surrounding zig and rust still leaves me with a bad taste because I also don't like how nonsensical topics like that influence what we do and what we (have to) care about on a day to day basis. That is just my opinion!
Something about bun always rubbed me up the wrong way (I even hate the name), but I couldn't really explain why.
Thankfully now I have some good material to post-rationalise my intuitive dislike
Mechanisms of beliefs, sense of identity and pride are behind of majority of projects including opensource. These are the same mechanisms which produce what you call "drama".
We can't have commited and involved people working on opensource stuff and simultaneously avoid drama when their sence of identity/beliefs/pride is devalued.
I didn't follow the thing too closely when it happened. Sure, I was aware of the big picture. But wow, I didn't expect that after all this noise there still hasn't been a release? That's just crazy to me.
I shouldn't be surprised though, of course. Giving any credit or slack to a high-valuation LLM company is a silly endeavor.
It was expected. These LLM rewrites seem to work amazingly at first and then you realize there is a ton of work remaining.
Author here: An apology on the graphs, they just count rust files touched in commits, not total commits. So if there were two commits and one touched 3 .rs files and another touched 2, it'd be counted as 5 for the purposes of the graphs. I may fix this later but, yeah.
Hope you find that job :) nice work experience, looks very ethical focused.
what kind of difference from the actual numbers does it result in?
Not sure! I cludged together a counter using git log. I could go back and redo it but I think the number would serve my point either way.
the author wrote a whole blog post asking how the bun rewrite is going and the answer from the thread is: nobody knows, including the author
"Nobody knows" is not a neutral sign however, Anthropic should be able to provide that visibility
That's absolutely correct!
This doesn't answer the question posed in the title unfortunately. I am none the wiser about how it's going. The author just speculates that the rewrite isn't actually complete.
> I am none the wiser about how it's going.
You and me both friend!
Coincidentally - I'm trying to get feedback on my own LLM rewrite project - MAME ROM machine code to Idiomatic JavaScript - the ability for an agent to understand blind code is remarkable.
But sadly HN is hiding my post... :(
https://news.ycombinator.com/item?id=49069383
EDIT: I'd love to hear why I'm downvoted.
It's pretty off topic/ irrelevant and it's self promotion.
An example of an LLM porting code is off topic to a project where the issue is entirely about an LLM porting code?
Can you explain that more?
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> we’re approaching $800k in money spent on this rewrite.
That’s peanuts, if not the shells of the peanuts, for a project and company of this magnitude
How does that help 99.9% of all other companies though?
Some thoughts:
- just because it doesn’t help 99.9% of the companies today it doesn’t mean it won’t help them tomorrow
- 0.01% of the companies employ a much bigger percentage of people
- 99.9% of companies won’t need to do a project of this magnitude
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Ohhhhh for a world where that's peanuts for an open source project.
If you’ve ever worked at a tech company you already know the answer without reading any further
Yeah, the answer is that it's gonna working fine for most users.
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Rust devs are so obsessed with writing things in Rust that Rust was re-written in Rust.