Is it easier to rewrite Bun than it is to rewrite Claude?
Claude Code uses Bun written in Rust now
371–380 of 920 posts
Re: Claude Code uses Bun written in Rust now
#372Drilling 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 missed things.
Rust does this automatically. It removes an entire class of errors from his backlog. From an engineering management perspective, this looks like a pretty good trade.
The bonus here is that compiler errors are exactly the kind of deterministic guardrail you need to put around coding agents. Claude works really well if you give it a way to test for correctness and "make it compile" is a pretty good target.
There's a general version of this: the artifact you expose plus the test you run on it. Deterministic tests turn stochastic output into a hard guarantee. Wrote it up here if useful: https://michael.roth.rocks/blog/verification-surface/
Re: Claude Code uses Bun written in Rust now
#373Earlier 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…
> $168k Billions of dollars of annual revenue go through Claude Code, and the people who work on it must be a lot of millions in headcount. The time matters a fair bit, it's probably time someone can't spend breaking things in the name of new features, but if rewriting the stack had even a tiny impact on retention or driving higher usage, it would pay back that $168k.
The company I work for is about 15mm into what is effectively a rewrite. Just a lone data point…
Re: Claude Code uses Bun written in Rust now
#374Earlier quoted context omitted.
I never knew that running an interactive program in my terminal would absolutely rinse my CPU and battery but that's what Claude, OpenCode and Ghostty have colluded to achieve. Even when the laptop is asleep overnight it's practically melting. I'm sure there was some logical reason for shoehorning web technology into this stack given that we have a good 40 years or so of experience with interactive terminal programs…
The fundamental problem with all Js based apps is how they are very single threaded. With js you get 1 thread at 100% utilization. Power usage and heat scale non-linearly with cpu utilization and 100% utilization on a single threaded js app means you will have ui lag. Other languages like golang would split work across 8 threads and have 8 threads at 20% utilization and this would result in less power usage. Claude C…
I'm not concerned with CPU use/wakeups while actively using it, but with it sitting idle doing nothing.
Re: Claude Code uses Bun written in Rust now
#375Earlier quoted context omitted.
I never knew that running an interactive program in my terminal would absolutely rinse my CPU and battery but that's what Claude, OpenCode and Ghostty have colluded to achieve. Even when the laptop is asleep overnight it's practically melting. I'm sure there was some logical reason for shoehorning web technology into this stack given that we have a good 40 years or so of experience with interactive terminal programs…
The fundamental problem with all Js based apps is how they are very single threaded. With js you get 1 thread at 100% utilization. Power usage and heat scale non-linearly with cpu utilization and 100% utilization on a single threaded js app means you will have ui lag. Other languages like golang would split work across 8 threads and have 8 threads at 20% utilization and this would result in less power usage. Claude C…
That’s not really a big issue. In major OS like the BSD, SMP implementation are not that old. If we can have a full OS running in single core mode, we can have an application being performant too. I’m currently running OpenBSD on 4 cores and it’s basically 99% idle.
Bad coding is just bad coding.
Re: Claude Code uses Bun written in Rust now
#376Drilling 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…
Zig (like C) is simply not a good language to use if you're going to do many small allocations with uncorrelated lifetimes. To write robust Zig (or C) code, you must manage lifetimes yourself, for example by grouping allocations on an arena or by having fixed buffers of "things".
You can just do that, and then Zig is really no less robust than Rust. But if you want to do "managed language" style allocation patterns (like what llms generally prefer), it doesn't make sense to use it.
Re: Claude Code uses Bun written in Rust now
#377Earlier 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. 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. 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 costs, can't be used as an excuse.
Re: Claude Code uses Bun written in Rust now
#378Maybe 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.
Why would rewriting Claude code, an app which probably has 30-40 (I might be significantly underestimating) extremely active contributors be easier than rewriting Bun, which has fewer contributors and almost certainly also less lines of code?
I'm doubtful that it has fewer lines of code, but even so, it is almost certainly less tricky and simpler code. You could also rewrite it in a higher level and more forgiving language than Rust (e.g. Go) and get huge improvements. The improvements would probably be much bigger than the improvements they have achieved at the JavaScript runtime level.
Re: Claude Code uses Bun written in Rust now
#379Earlier 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. 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…
Yeah, this is what I’m trying to get at. There’s two arguments in competition: 1. LLMs make it cheap (in the time sense) and easy to build 2. Rewrites and/or writing something in a native app or program is harder and more time consuming I think I am willing to take it as an axiom that a native version of CC would be superior from a user perspective. Performance, etc. I just don’t see how one can say that building thi…
>2. Rewrites and/or writing something in a native app or program is harder and more time consuming
Why would it be harder and/or more time consuming rather than the opposite? It's like having full specs and a full test-suite to match against the result you want.
Re: Claude Code uses Bun written in Rust now
#380Maybe 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.
Should have done it in C++ with SDL3.