How is the Bun Rewrite in Rust going?

https://lockwood.dev/ai/2026/07/27/how-is-the-bun-rewrite-in-rust-going.html

Comments

SquareWheelJul 27, 2026, 12:09 PM
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.

usef-Jul 27, 2026, 12:13 PM
Yes, I was actually wondering if all the attention also attracted new contributors too.

They also have made a release, in a sense, since they moved all Claude code users to it. (And apparently no one noticed).

I think they're taking things "gradually" as they are under a lot of scrutiny and no rush for release.

abalashovJul 27, 2026, 11:52 AM
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.

eelkeJul 27, 2026, 12:11 PM
While the Rust rewrite branch might not be officially released, Anthropic and (I assume) the Bun team considered it good enough to ship to millions of Claude Code users (since v2.1.181) for over a month now!
muglugJul 27, 2026, 11:55 AM
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.

virajk_31Jul 27, 2026, 12:03 PM
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.
cowlJul 27, 2026, 12:06 PM
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.
rk06Jul 27, 2026, 12:02 PM
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.

davidgtongeJul 27, 2026, 12:10 PM
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.

reactordevJul 27, 2026, 12:12 PM
[delayed]
nullsanityJul 27, 2026, 12:14 PM
[dead]
abalashovJul 27, 2026, 11:58 AM
> 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.

muglugJul 27, 2026, 12:05 PM
Maybe they will!

Are you expecting them to live-tweet their work or something?

reliabilityguyJul 27, 2026, 11:55 AM
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.
TinkeringzJul 27, 2026, 12:08 PM
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.

reactordevJul 27, 2026, 12:14 PM
[delayed]
HasnepJul 27, 2026, 12:13 PM
I think they missed a $ sign, i.e. they meant $100k of tokens
yearesadpeopleJul 27, 2026, 12:01 PM
> _"...Canny..."_

What a time to be alive

rob74Jul 27, 2026, 12:08 PM
Yeah, I noticed that too and kept wondering who this Canny was that the author wants to be? Felt a bit un-Canny...
tomlockwoodJul 27, 2026, 11:51 AM
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.
alienbabyJul 27, 2026, 11:57 AM
what kind of difference from the actual numbers does it result in?
tomlockwoodJul 27, 2026, 12:00 PM
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.
vortegneJul 27, 2026, 11:59 AM
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.

brapJul 27, 2026, 11:50 AM
If you’ve ever worked at a tech company you already know the answer without reading any further
raincoleJul 27, 2026, 11:52 AM
Yeah, the answer is that it's gonna working fine for most users.