My Thoughts on the Bun Rust Rewrite

> So, when the Anthropic aquisition finally happened, we at ZSF breathed a sigh of relief. When the donation silently stopped, our bank account was ready for it. When they neither canceled their monthly meeting with us, nor showed up, we were not surprised. The relationship was over.

Seen this time and time again, project/organization gets taken over, and everything "good" they did doesn't get exited with fanfare or anything, just silently dropped as your benefactor starts silently ignoring you.

I'm really happy they saw the writing on the all and were prepared for the inevitable, a really great lesson you shouldn't need to learn yourself the hard way, and FOSS project relying on one/two big donators should take heed, we'll see a lot more of this in the developer tooling ecosystem moving forward for sure.

I found this post very refreshing! I’m sure it would have been very tempting to one-up the “PR-speak” of the Bun post. Likewise, it would have been very tempting to include the same set of facts that reflect negatively on Jarred, while studiously concealing one’s own opinion (eg “I heard people called him a stinky manager. I am not saying that, other people are, but I’m not”). I appreciated that it was just … genuine.

Not sure a personal attack against Jarred really helps the case for using Zig. He could have and should have focused on the language and not “a stinky manager”. Honestly, this makes me want to steer clear of Andrew as much as Jarred.

> Two, I actually don't have any personal criticisms of Jarred

That’s quite a statement to make at the end of a post that seems to contain little else…all just thinly veiled.

Saying someone has „beginner energy“ but reframing it as a faux positive (this person fails and thus learns)

Or saying the grapevine says someone is a „stinky manager“? Basically I’m not saying this person is bad it’s just that I need to bring up on this blog that everyone agrees this person is bad.

All seems to be in very poor taste even if true…

It's hard, in my opinion, to lend credence to the author here when they decided to devote the first and largest section of their article to an incisive display of speculative ad hominem.

Would have been a great opportunity to outline the benefits of Zig! I've been keen to pick Zig up recently due to mitchellh's evangelism and inspiring writing on the subject.

This article puts me off learning Zig.

> I actually don't have any personal criticisms of Jarred

The whole post felt like a personal criticism of Jarred.

> The main problem, however, was code quality.

> The sleight of hand misdirects the reader away from the main way bugs are eliminated: by dedicating engineering resources to it.

Perhaps the amount of bugs comes from using a C-like language that requires meticulous manual care to avoid writing runtime bugs.

Even C++ would be a safer choice because of RAII.

When you have to dedicate significant resources to avoid/fix runtime issues that are made impossible at compile time by other languages, the programmer isn't entirely at fault.

This is unprofessional and embarrassing for Zig.

I know very little about Jared but his article yesterday, which I read, seemed appreciative of Zig. I now learn he's donated significant chunks of money to them.

This entire article is publicly and personally attacking him for choosing a different product.

It's insane to me that Andrew thinks this post will somehow exonerate Zig when it really just makes them look childish. Or maybe he doesn't care, and just wants to attack Jarred?

There are astute comments about the post's tone elsewhere in this thread[0]

But this killed my hopes for Zig.

The drama is fun, and Andrew is maybe even admirable in his earnest, but this just isn't the kind of professionalism needed for a serious project. I know that's boring and uninspired, but that's what I want my tech stack and it's management to be.

Also, maybe Jarred was a net negative, but bun was also a really big project using Zig, and the project leaving isn't as good for Zig as Andrew is making it seem. It genuinely seems he's putting a lot of priority on purity and ideology over just growth of the language. And I am sorry, but adoption and reaching critical mass is an important part of a serious programming language.

[0] esp. nilirl.

To me, this whole effort of rewriting Bun from Zig to Rust looks like a big marketing move. The question is: if Anthropic AI is really that powerful, why not just fix the bugs and give it the more ambitious task of redesigning the existing Bun Zig codebase in a way that eliminates not only the current bugs but also prevents similar ones from happening in the future?

Despite stated otherwise in the post, this is a personal attack.

Anyway, let's try to discuss something more technical: I predict Zig will lose steam, and in 2027, will lose relevance:

1) It's hardcoe Anti-AI 2) It's moved to Codeberg 3) It doesn't have the momentum to sustain the disadvantages of these two decisions

The project will in max 2 years make a blog post, not admitting to their mistakes, telling themselves that Zig is a success, despite the industry having moved on.

> The post claims they were fuzzing their Zig code, while during our calls the whole Bun team told us that they were not fuzzing anything. This appears to be an outright fabrication.

Interesting I wonder if its something Jarred did locally or something else that was just not widely done by the whole team? I dont like to make bad assumptions about devs or dev teams without first asking. I owe credit to HN for one of the guidelines which states something like do not assume intentional malice in comments, I feel like we assume the worst in general about other devs, but people are imperfect and make mistakes.

That said as others noted this post could have been written a bit differently while still pointing out genuine issues. The ad hominem attacks are a bit unnecessary and add nothing of value to what could have been a better response.

I was wrong to be upset this whole time that the rewrite would hurt Zig. This is one of those rare occasions when I’m glad I was wrong. Interesting insights.

articles like these are needed - if you've to call people out - do it.

the tech industry's fake politeness has caused pain and confusion.

& yeah - I had already stayed off Bun before the whole rewrite, but now more reasons.

> You can imagine how we might want to put some social distance between ourselves and a project whose irresponsible software engineering practices invite the exact kind of criticism that people are eager to level.

The other (very salient) points notwithstanding, I'm afraid this quote shows that Zig hasn't learned a lesson that other languages of its generation (and older) have: if a project's memory safety depends only on "responsible engineering practices", then that project most likely won't be memory safe. Quoting the "swiss cheese" model used in risk management: one slice of cheese (engineering practices) just isn't enough if you want to be reasonably sure your program is memory safe.

A better title would be 'My emotions on the Bun Rust Rewrite', since the article feels like an emotional reaction rather than a thoughtful analysis of the situation. Give it some time..

I'm rooting for Zig either way, even though I have nothing against Rust and I don't directly use bun.

well, for me personally, "the" Zig project is not Bun but Ghostty, and it always has been.

yeah, Mitchell is very pro-AI, but he is thoughtful, and he sometimes highlights the difference between Zig's and Ghostty's approaches to LLMs (outright ban vs taming)

Anyone who would write an article like this is much more distasteful to me than anything Jarred did.

> The sleight of hand misdirects the reader away from the main way bugs are eliminated: by dedicating engineering resources to it.

Why don't YOU spend the engineering resources to add RAII and a borrow checker instead of blaming your users?

Dedicating most of the article to a personal attack and then finishing by saying that you don't have anything against the person is a bit of an odd sequence.

I’m not sure why this post even exists? It feels completely unnecessary. Don’t get me wrong, I like drama as much as the next guy, but it didn’t have to be public imo

> The sleight of hand misdirects the reader away from the main way bugs are eliminated: by dedicating engineering resources to it.

I was on a platform team and I had a constant backlog of bugs (introduced by others) that I was working on and the two most impactful things for preventing bugs were Typescript and Cypress (playwright-like testing before playwright).

I've dealt with many shitty code bases and the only way that worked for removing bugs was automation. It didn't matter how many bodies you threw at the problem.

> Then why are you saying you have so many annoying bugs in the Zig code? What happened to the test suite being sufficient to catch everything?

You can't use tests for trying to catch use after frees and other memory bugs for the same reason you can't use unit tests as a replacement for type checking, the combinatorial explosion of possible inputs into functions makes unit testing types across an entire project impossible.

Anyway, Jared donated $60k a month to this project and tried to resolve this in the most diplomatic way possible and still got personally attacked. The lesson from this article is don't donate to the Zig project because if you migrate away from it they will try to ruin your reputation.

I'm glad LLM coding exists for people who want to move at an insane superhuman speed (perhaps they're trying to achieve escape velocity and launch into the stars or something) so that they don't grind down their fellow humans.

You can either do local optimization - a single individual moving as fast and as hard as humanly possible, or global optimization - a team working together and amplifying each other's efforts to produce something that is greater than the sum of its parts.

While I agree that the Zig code in Bun could be better, and that the Silicon Valley pressure to move fast and break things prevented a lot of suggested improvements, this feels like the same argument as people who write C or C++ where people think they wouldn’t make mistakes.

> We became increasingly horrified at the programming practices we saw in Bun's codebase. Hacks on top of hacks. Abuse of assertions. Most of all, recklessly speeding past feature after feature with very little time taken for reflection and elimination of bugs and technical debt.

The vast majority of software is written by businesses, who have to cater to the lowest common denominator in their code base, and who are not incentivized to go slower. That is a reality of what we need programming languages to help with in 2026. I've never met a professional programmer that has not seen or said the same thing about a code base that they've worked on.

New programming languages need to contend with that reality if they want to be adopted en masse. If not they are doomed to not be adopted (which is okay I've created many programming languages that are just for me). But if a programming language in never adopted then the supposed benefits or improvements of the language never trickle down to us the users of the software, so they just remain interesting ideas (which again is okay).

Andrew kelley runs a tight ship, and his foundation does not need a lot of money to keep going, but he has talked about how working on all the organizational transparency is not his favorite part of the project, and I can see why a lot of young programmers wouldn’t want to go that way.

It's more like a transpile, far from idiomatic rust.

While I understand ZSF's bittersweet relationship with Oven and agree to several points (especially preparedness), this writing is badly structured and that shows something. Hope to see him turning around.

When you said that “His code was slop well before LLMs” got a good cackle out of me.

The fact is, most people don’t have taste and haven’t had taste, LLMs just amplify what was already there. Good taste is good taste, slop is slop, and shit is shit.

Glad you guys were able to go your separate ways.

It feels like the first half of blog post is less of "thoughts on the Bun Rust Rewrite" and more "I don't like Jarred, he's a bad programmer and manager".

Maybe I'm wrong, but it strongly feels this way. I'm not saying that Andrew is right or wrong, it's just that you could throw out most of the first half of the post and not lose anything actually on topic.

> But having graduated from the Thiel Fellowship school of thought rather than university, he was essentially groomed from a young age into uncritically embracing the Silicon Valley mindset, and he took venture capital.

> Jarred was a stinky manager. Poor communication, unrealistic expectations, low empathy, no experience. Just a total shit show, from an employment perspective.

> Jarred was already writing slop well before he had access to LLMs

The post reads like someone who is quite upset but trying to maintain professionalism. The mask slips throughout.

The points seem valid, however, and I will likely steer clear of Bun.

I desperately hope that the Andrew Kelley style of software engineering will survive all of this; that users will continue to value quality and not be content with slop. This, of course, presumes that products built fully by agents will produce sub-par quality in the future. If they will be able to manage to glue all of this slop together without the project collapsing in on itself, none of this will matter. I just hope that this isn't the future of the industry.

The project needs an adult in the room - preferably someone less on the spectrum - who approves this content before it goes out. This reads as an incredibly butthurt, petulant rant, authored by someone deeply hurt that users are putting all the blocks into the square hole. Andrew would have been served better by a Linus-style curt takedown, rather than this drivel.

This is 2017 Biden vs Trump for people who know who Godbolt is

Zig is getting that Elm, etc vibe. Genius/visionary BFDL who's also personally incapable of leading the project towards healthy long-term viability.

Say what you will about Matz or José Valim, I don't think they'd ever write a "and don't let the door hit you on the way out" screed full of personal attacks ("stinky manager", "writing slop", "a total shit show") against a person who led a very prominent project and financially supported the language.

I for one appreciate a public figure with a wildly opposed mindset to the Silicon Valley/VC-Funded/Ultrascaling/whatever crowd.

The pushback is warranted and on point, especially the technical points. It has taken a suspicious amount of time to produce the fabled blog post which I don't think states almost any new information beyond what Jarred has already shared on twitter. The one (and very interesting) exception is the theoretical price of the rewrite via the API pricing.

>We became increasingly horrified at the programming practices we saw in Bun's codebase. Hacks on top of hacks. Abuse of assertions. Most of all, recklessly speeding past feature after feature with very little time taken for reflection and elimination of bugs and technical debt.

I'd like to know what the poor code quality in Bun looks like. Does anybody have concrete examples?

I read the post and roughly summarized it as:

1.It felt uncomfortable that Bun was presented as a representative example of Zig. From the internal Zig perspective, it looked more like a bad example of how to use Zig.

2.It felt uncomfortable that they spoke as if Rust prevents things that could actually be handled by Zig's style guide.

3.I(OP,andrewkelly) don't think badly of Jarred as a person, but after signing a contract with VC, the management side has been poor.

4.The Bun documentation looked like marketing.

5.Bad contributions driven by AI came through indirect promotion of Bun, which attracted interest from people after it was acquired by Antropic.

I understand that it's burdensome to see Bun as Zig's representative success story, and I get the wish not to see Rust rewrites through a lens of language superiority. But on the flip side, I'm not sure I would have ever learned about Zig if not for Bun.

While the criticism is valid, I also understand Bun's position. After all, Antropic's acquisition of Bun was ultimately about showing that even a 'new language' can be used effectively with AI, and that's precisely where the friction arose.

I think the refusal to accept AI from a purely human programmer perspective is a matter of personal values, and I find the Zig team admirable on a human level. (Though I'm an active proponent of AI, so my view differs.)

Both sides have valid points, but sometimes I wish someone would turn the emotional and political dynamics of open source into a novel. I think it would be fascinating

So bun went from bad Zig code to absolute slop Rust code?

Is the bun rewrite actually done? There's no tag for the release, and as it stands robobun has almost 1.3k open PRs on the repo: https://github.com/oven-sh/bun/pulls/robobun

It doesn't look done.

And it looks like work on the rewrite began in early may: https://github.com/oven-sh/bun/commit/46d3bc29f270fa881dd573...

So... its more like a 2 month rewrite that is definitely not done yet????

> he could have easily achieved a solid living via crowdfunding, even for San Francisco standards.

That sounds completely surreal. Is Bun really used that much?

I notice something more interesting. This post shows Andrew to not only personally criticise Ben but also clearly shows an ideological stance against AI. I can see it from multiple angles - refusing AI PR's, refusing Anthropic's donation and multiple other things.

Either this ideology helps Zig position itself as a hand crafted language. Or this ideology is self defeating.

This is quite an interesting read from Andrew's perspective. But one line tells me everything I needed to know.

> The blog post is expertly written. It's almost like the marketing department of a trillion dollar company has a lot of money riding on this article.

Even Andrew knew that this was going to be Anthropic's marketing opportunity for AI to rewrite Bun from Zig into Rust. This post from Jarred says it all. [0] If you have access to hundreds of billions worth of resources (infinite tokens and compute), they don't care what others think and some relationships are just cheap to discard.

Like I said before in [1] and [2], Bun (now Anthropic) does not care about you. They did this to market the capabilities of their AI models and this rewrite was an example of that in broad daylight. Even if Zig allowed AI generated contributions, this move was going to happen anyway.

I cannot believe that many commenters in [0] at the time did not see that this rewrite was eventually going to happen.

[0] https://news.ycombinator.com/item?id=48019226

[1] https://news.ycombinator.com/item?id=48240829

[2] https://news.ycombinator.com/item?id=48073893