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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

#481

Post by simonw »

vintagedave wrote: post #431
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.

I asked this in a thread with a CC author a few months ago (I felt — and hope — very politely, with similar background.) No reply. https://news.ycombinator.com/item?id=46716974

At a guess it's because Boris literally wrote a book on TypeScript: https://www.oreilly.com/library/view/programming-typescript/...

Re: Claude Code uses Bun written in Rust now

#482

Post by simonw »

shafyy wrote: post #444
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. Does anybody really believe that it only took 11 days, one engineer and $168k in tokens?

It played out in public on the GitHub repository, so yes.

Re: Claude Code uses Bun written in Rust now

#483

Post by harrisi »

Maybe I'm taking crazy pills, but I swore there have been very similar comments I've seen as the current top post by weakfish:

> 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 turns out, there's some similar sentiments in the last year ish:

https://news.ycombinator.com/item?id=47043325

https://news.ycombinator.com/item?id=47105720

https://news.ycombinator.com/item?id=48001113

https://news.ycombinator.com/item?id=46134570

https://news.ycombinator.com/item?id=46124596

I'm not a fan of any of the technologies, companies, or people related to this. I just couldn't shake the feeling that I've seen similar comments.

September and all.

Re: Claude Code uses Bun written in Rust now

#485

Post by simonw »

eventhorizon77 wrote: post #454
ethbr1 wrote: post #192

Earlier quoted context omitted.

Afaik, under current US law (Thaler v. Perlmutter 2025^), "the Copyright Act of 1976 requires all eligible work to be authored in the first instance by a human being". With regards to AI-generated code, this means the copyrightability (at all , not with regard to who owns it) turns on whether or not a human was substantially involved in its creation. Existing decisions require evidence of pretty heavy and continued h…

Couldn't it be argued that Bun-Rust is still MIT licensed, because the old implementation was "in the first instance" authored by a human? All the machine did was translate it. I think it's the "infringing usage" question that is more interesting. If the LLM trained on GPL-derived code, what does that mean for the end result?

"If the LLM trained on GPL-derived code, what does that mean for the end result?"

Either it means nothing at all, or it means that a substantial portion of the code produced at some of the world's most valuable companies over the last two and a half years is GPL.

Re: Claude Code uses Bun written in Rust now

#486

Post by harrisi »

harrisi wrote: post #483

Maybe I'm taking crazy pills, but I swore there have been very similar comments I've seen as the current top post by weakfish: > 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. >…

I don't want to edit this to change the narrative, but I wanted to clarify that I'm not not a fan of all of the technologies or people related to this. As far as compan{y,ies} go, though, well..

Re: Claude Code uses Bun written in Rust now

#487

Post by TheRoque »

embedding-shape wrote: post #2

> For me this outputs Bun v1.4.0 (macOS arm64). The most recent release of Bun on GitHub is currently v1.3.14 from May 12th, so that v1.4.0 version number in Claude supports them shipping a preview of a not-yet-released Bun version. And so, the FOSS project "Bun" silently dies in darkness and is now something completely else. I'm glad I still had "Investigate if Bun is worth it" on my TODO list and hadn't yet gotten…

I had "investigate if bun is worth it" too, and decided not to use it, but instability was one of the reasons. So it feels it was the right move.

Re: Claude Code uses Bun written in Rust now

#488

Post by simonw »

sensanaty wrote: post #417
simonw wrote: post #368

Earlier quoted context omitted.

I've not made any money at all from Anthropic. You can see my list of previous weekly blog sponsors here: https://simonwillison.net/dashboard/sponsor-history/ None of them get any influence on my content. That would hurt my credibility, and my credibility is the reason my site is worth sponsoring in the first place. Honestly, if OpenAI or Anthropic offered to sponsor I'd probably turn them down. The optics of taking…

Fair, that rules out "Anthropic pays you directly." But look at your own disclosure page [0]: OpenAI paid you for your time at a GPT-5 preview, and you regularly get early access, embargoed previews, and free API credits from OpenAI, Anthropic, Gemini, and Mistral. So "I've made no money from Anthropic" is narrower than it sounds, access and preferential treatment are compensation too, even if cash didn't directly ch…

Your comment here is fair, and it's why I take my disclosures seriously.

Nobody is unbiased, no matter how hard they might try. I like to get my information from sources where I understand their motivations, so my approach is to try to make my motivations as clear as possible.

(That's why I spend an unreasonable amount of energy arguing with people on Hacker News who call me a shill!)

Re: Claude Code uses Bun written in Rust now

#489

Post by coldtea »

hluska wrote: post #467
coldtea wrote: post #377

Earlier quoted context omitted.

> 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…

Do you know their entire roadmap? If not, maybe different people prioritize things differently when they see their full strategic position.

How is that relevant to my response?

The argument I responded to argued that cost might be the prohibiting factor. I'm saying that for them, the costs mentioned are negligible.

Re: Claude Code uses Bun written in Rust now

#490

Post by jstummbillig »

coldtea wrote: post #295
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…

> 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. Your counter argument would be valid for a 2000 or a 2020 business decision about some tech stack. 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 w…

> 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.

Eventually? I am sure they would agree. Currently it's you (and lots of people like you) who are doing the supposing, not Anthropic.

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