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Claude Code uses Bun written in Rust now

simonwillison.net

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Re: Claude Code uses Bun written in Rust now

#471

Post by theshrike79 »

gchamonlive wrote: post #424
mrothroc wrote: post #372

Drilling into the original article where Jarred explained the reasoning behind the change, It's pretty clear that under zig the team was doing things by hand that are automatic in rust. Humans and agents share one thing: they are both non-deterministic. He talks about the issue of tracking memory lifecycles manually in zig so it can be explicitly freed. As expected, this leads to a long list of bugs where people miss…

> Rust does this automatically. It removes an entire class of errors from his backlog. Even with the huge amount of "unsafe" rust currently in bun? https://news.ycombinator.com/item?id=48967630

You think it’ll all stay there?

Of course they’ll iterate and remove the unsafe bits which were necessary for the transition

Re: Claude Code uses Bun written in Rust now

#472

Post by solumunus »

troupo wrote: post #421
solumunus wrote: post #354

Earlier quoted context omitted.

I think the point is that people still continued to use it above everything else regardless.

Because there's no legal way to use Claude Code on subscription otherwise

Exactly. Their tech choices were not an issue because other things mattered more to users.

Re: Claude Code uses Bun written in Rust now

#473

Post by anamexis »

tripleee wrote: post #396
anamexis wrote: post #276

Earlier quoted context omitted.

What do you mean in spite of their tech choices? When have the tech choices ever been an issue in the lifespan of Claude Code? From where I sit, it seems like their tech choices enabled them to create an industry-defining product.

I mean people are using Claude Code because of their underlying LLM - they'll put up with Claude Code. There's no other real option to get Opus at a reasonably affordable price without CC. Most people would choose to swim a lap through a pool of pee to get a billion dollars at the end. The pool of pee itself wasn't the once in a lifetime opportunity (for most). Sorry, I'm bad at analogies.

I may not be the standard case, but I use Claude Code over Codex, OpenCode, Amp, etc primarily because of the UX, not the models or pricing.

Re: Claude Code uses Bun written in Rust now

#474

Post by georgemcbay »

pdimitar wrote: post #345
benoau wrote: post #273

Earlier quoted context omitted.

> They succeeded in spite of their tech choices. Or those choices just don't matter, it's fundamentally just "tabs vs spaces".

As much as an enthusiast dev like myself hates it -- this is innately true, way too often. I am 46 y/o and still excited to code and solve problems with code and I still have trouble to admit to myself sometimes that people make dozens of millions with PHP and the tech hardly matters when you can throw bodies at the problem (and when that throwing of bodies at the problem actually solves it, of course).

> I still have trouble to admit to myself sometimes that people make dozens of millions with PHP

Or many billions. eg. Facebook was originally written in PHP.

As a 52 y/o who cares deeply about software development as an art I don't have trouble admitting that the tech hardly matters relative to the economics, that was obvious to me very early in my career.

I have just never really cared because there has always been a path where you can have a decent career being paid to work on and with good technology in spite of the fact that the technology wasn't important to the economics.

I do fear that the rapid adoption of LLMs will probably cause the path I took to narrow considerably. There will likely be less companies willing to pay people to work on elegant technology when they are all competing against endless code generation machines (and this is assuming software companies can exist at all in this future). But at my age that's more of a concern for younger people than me.

Re: Claude Code uses Bun written in Rust now

#475

Post by wonnage »

switz wrote: post #236
weakfish wrote: post #212

Maybe I’m taking crazy pills, but I’m still stuck on “why the hell does a TUI need to run in terminal React by way of JavaScript” The fact that Anthropic felt the need to buy a runtime so they could make their TUI better speaks more to the quality of engineering than anything else IMO. If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.

It largely works and it's a massive business success. This is the classic engineer asking the 'why this technology?' to what amounts to a business question. They chose it early on, it works, and it makes obscene amounts of revenue. End of story. That doesn't mean it was the "greatest" choice, or has a perfect technical architecture. Rewrites are never easy, even the bun rewrite. But a non-UI developer tool with a rig…

This is a useless post-hoc rationalization. "It worked out, so it doesn't matter". You're trying to galaxy brain yourself into ignoring the obvious conclusion.

The point is that if you were starting a new TUI LLM harness today, you would basically use CC's architectural decisions as a guide for what not to do.

Re: Claude Code uses Bun written in Rust now

#476

Post by pronik »

layer8 wrote: post #100
atonse wrote: post #18

Earlier quoted context omitted.

It’s made absolutely no negative difference, as we’ve seen in the real world in the last 60 days since the merge. I feel weird having to defend reality; reality being that it was merged nearly 2 months ago and tons of people have had their pitchforks out without a shred of actual evidence that this made bun worse in any measurable way. But they still insist it was a mistake. I’ve never met Jared or the bun team but I…

> who cares what language a JS toolset is written in? Anthropic, apparently, not the least because they blanket-closed all issues submitted before the rewrite. If the language were irrelevant, it shouldn’t matter for the existing unfixed issues.

> blanket-closed all issues submitted before the rewrite

You'll need a citation for that. While I'm still not sure whether Claude Code's issue tracker is worth much (Anthropic doesn't seem to engage with individual issues a while lot), it still has 5k+ open issues ranging back to March 2025. Bun also still has all of its Zig-timeline issues, all 5k+ of them. So what's this about?

Re: Claude Code uses Bun written in Rust now

#477

Post by pronik »

bmitc wrote: post #220
atonse wrote: post #18

Earlier quoted context omitted.

It’s made absolutely no negative difference, as we’ve seen in the real world in the last 60 days since the merge. I feel weird having to defend reality; reality being that it was merged nearly 2 months ago and tons of people have had their pitchforks out without a shred of actual evidence that this made bun worse in any measurable way. But they still insist it was a mistake. I’ve never met Jared or the bun team but I…

The outrage was more how the rewrite was communicated and defended, which was objectively poor.

Which was completely bonkers -- it happened completely in the open, people were just outraged that something like this happens without asking them and not on a schedule they perceive as adequate. Most of them haven't really grasped what was happening and why. Many still don't.

Re: Claude Code uses Bun written in Rust now

#478

Post by wild_egg »

vmg12 wrote: post #443
anthk wrote: post #423

Earlier quoted context omitted.

Sorry, but nope; Golang there would be there a beast doing that in a much, much faster way. Not to mention C/C++ with NCurses.

> If you think this is actually nothing, prove it. Put the code up on github that shows taking a constant random stream of markdown, code, and diffs and displays it in the terminal can be done cheaply on a single thread. Put up the code and prove it. We already know exactly how fast golang is in comparison to nodejs on basic numeric computations, it's roughly 40 to 50% faster.

https://pierre.computer/writing/on-rendering-diffs

Re: Claude Code uses Bun written in Rust now

#479

Post by mixmastamyk »

vmg12 wrote: post #412
wild_egg wrote: post #394

Earlier quoted context omitted.

No, the fundamental problem of these apps is that they are, for no reason, pretending they need a high powered game engine rendering loop. They don't. It's a text printout of history with some hotkeys for mode switches and such. "rendering in a single thread" should never be an issue because it should never be "rendering". It needs to stream text to stdout. That's been a solved problem for 50 years and now it takes 2…

Drawing to the terminal / rendering / whatever, this is all arguing semantics and very uninteresting and not insightful. > they need a high powered game engine rendering loop Don't believe the bs on twitter. Claude code source was leaked, there is no high powered game engine rendering loop. > It needs to stream text to stdout These apps are doing real work taking text that is streaming in and doing syntax highlightin…

Stuff doable on a pentium 90, and before that, just slowly.

Re: Claude Code uses Bun written in Rust now

#480

Post by tacitusarc »

switz wrote: post #236
weakfish wrote: post #212

Maybe I’m taking crazy pills, but I’m still stuck on “why the hell does a TUI need to run in terminal React by way of JavaScript” The fact that Anthropic felt the need to buy a runtime so they could make their TUI better speaks more to the quality of engineering than anything else IMO. If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.

It largely works and it's a massive business success. This is the classic engineer asking the 'why this technology?' to what amounts to a business question. They chose it early on, it works, and it makes obscene amounts of revenue. End of story. That doesn't mean it was the "greatest" choice, or has a perfect technical architecture. Rewrites are never easy, even the bun rewrite. But a non-UI developer tool with a rig…

This is the “eating yogurt with a hammer” argument. Yes, of course you can do that. Yes, the yogurt gets eaten. It’s just… you see someone eating yogurt with a hammer and it’s hard not to wonder wtf is going on.
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