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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

#501

Post by vips7L »

azeirah wrote: post #321
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".

Eh, the rendering of Claude Code is genuinely such a mess. I have quit claude code over it because when used as a terminal in PHPStorm it sometimes gets so bad that it becomes hard to use. This isn't a minor nitpick, it's a pretty major UX issue. Not saying it's like a massive business downside because I'm just one of a few users, maybe this affects their bottom line a little bit, but probably not by much. Regardless…

You don’t have to use these “tools”.

Re: Claude Code uses Bun written in Rust now

#502

Post by jbvlkt »

coldtea wrote: post #377
pdimitar wrote: post #342

Earlier quoted context omitted.

> But the whole point of their product is that it supposedly nullifies such "business" concerns around the use of technology, by making it cheap and fast to build whatever you like automatically. This is a spectrum, it's not just 0% vs 100%. Even Fable frakked up a few things really badly in my professional work (though to its credit after a very detailed 2h chat it self-corrected and fixed all the blunders). I would…

> Reminder that the Bun's Zig-to-Rust rewrite took 11 days with dozens of agents working 24/7 and the author put the cost they'd pay (if they had to pay) at about $168k. For an entity like Anthropic that's not even the cost of a single developer for a year. It's closer to what they pay a chef on premises. That the showstopper for a better Claude agent is that they'd need to pay $168k or event $1M or even $10M in cost…

Lets see what happens in the future. From my experience cost of maintaining this amount of shitty code explodes pretty quickly. We will see in a few years if SW development in all phases using agents is that much automated and easy as people now predict.

Re: Claude Code uses Bun written in Rust now

#503

Post by aurareturn »

GuB-42 wrote: post #209

Why all the mess with Bun? Couldn't they have rewritten Claude Code in Rust directly? No more need for a JS runtime, better performance, etc... If their agents can do Zig to Rust, why not JS to Rust?

Is Claude Code bottlenecked by performance?

I think a JS runtime is fine because the ecosystem of tools is very large and plugins are easy.

Re: Claude Code uses Bun written in Rust now

#504

Post by vips7L »

jeremyjh wrote: post #299
bwfan123 wrote: post #255

Earlier quoted context omitted.

So, you have a vibe-coded TUI which happens to work, and then, as a workaround you vibe-translate its engine to make it more performant. Where does that leave you ? Basically, fully dependent on AI to fix whatever breaks. Workaround on a workaround is the way I see it, and it aligns with the AI design mentality in general. For a variety of usecases, this might still be a win in terms of overall cost. But, for softwar…

Bun was not ported to Rust for performance reasons and its not clear to me how anyone can think it was. The reason they've given is memory safety.

It was ported for vibe reasons.

Re: Claude Code uses Bun written in Rust now

#505

Post by rho138 »

CrimsonRain wrote: post #268
rho138 wrote: post #50

Earlier quoted context omitted.

That sounds like a massive waste of finite energy and compute resources.

That's like saying let's stay with horses. We'll develop faster and better tech. We'll find resources to feed that. Use that to build better. Access better resources. We'll mine asteroids. We'll harness much more from the sun. The factory must grow.

Is that before or after the earths atmosphere acidifies for humans and our bodies can’t hold enough phosphorus or calcium for basic metabolic tasks? You have until 2050:

https://doi.org/10.1007/s11869-026-01918-5

Re: Claude Code uses Bun written in Rust now

#506

Post by abc42 »

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.

>If rewrites are so easy, why not rewrite CC in a native language? Would’ve been a hell of a lot cheaper.

Yeah, good question. OpenAI decided to rewrite Codex in Rust about a year ago[0].

In fact, since rewrites are that easy, what do we need Bun for? Why doesn't everybody just port all of their Javascript code into Rust?

[0] https://github.com/openai/codex/discussions/1174

Re: Claude Code uses Bun written in Rust now

#507

Post by BoppreH »

yojo wrote: post #357
switz wrote: post #236

Earlier quoted context omitted.

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…

I have been working all day every day in Claude. I loathe their bug-ridden UI. Every release is a new crop of bugs, sometimes the old ones get fixed, usually not. Any kind of scrolling back, copying text, using their menu system - basically anything that isn’t typing characters has had/still has unaddressed bugs. OpenAI shipped a competitive model and I’m over in Codex now. I have yet to hit a bug. If you’re holding…

> basically anything that isn’t typing characters has had/still has unaddressed bugs.

Oh, that's buggy too. I just tried Claude Code on win10 powershell, and the first typed character goes in the wrong spot and can't be backspaced.

It is by far the the least reliable program on my machine, and every time I have to interact with it I feel like walking in eggshells.

Re: Claude Code uses Bun written in Rust now

#508

Post by pjmlp »

BigTTYGothGF wrote: post #457
pjmlp wrote: post #326

Earlier quoted context omitted.

There is more to it even, the UNIX and C founders arrived to Go, before retirement, after a few other interactions. AT&T was the one doing the Cyclone research. And then we have a bunch of folks assuming they know better about C that its own authors?

> And then we have a bunch of folks assuming they know better about C that its own authors? Barthes aside, C's changed a lot in the years since they left.

Yes they stopped caring after C89, Plan 9 C compiler was a mix of C89 with extensions.

Still they are the authors, and withdrawing from WG14, going their own direction with Alef, Limbo, and finally Go, kind of proves the point they considered C done for its original purpose.

Re: Claude Code uses Bun written in Rust now

#509

Post by pianopatrick »

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.

As a counter argument - I assume that Anthropic is using AI to write Claude Code.

I've read and heard in videos that Javascript is a pretty good language for AI to write code in. Apparently this is because there is so much training data out there. Also Javascript avoids problems of multi threading and memory management that can mess up the AI in other "more performant" languages.

So maybe Javascript is not the worst choice for writing software fast with AI

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