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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

#141

Post by nirui »

All the emotion of speculations aside, how it runs? It boots faster yeah, but what about RAM and CPU usage? Weird dead loop or dead locks?

If it run as good as before or even better, then that's kinda impressive.

I'm a developer so I really don't like it when AI might took my job, but if everyone on this planet could create a software for themselves exactly as how they wanted with just a few simple demands, that will change the world for the better.

Think of it as a democratization of technology. You don't want Microsoft stealing your data? Just ask a AI to write an OS for you. You don't want Google to listen to what you're saying? Just ask a AI to design a phone for you. If one day the AI ended up doing that, it will be the ultimate technology self-sufficient. In front of that, your job security is insignificant.

It is also why keeping the tech open source is that much important. Otherwise, it's still the same old shit again and again, and, you lose your job too.

Re: Claude Code uses Bun written in Rust now

#142

Post by nicce »

simonw wrote: post #122
embedding-shape wrote: post #115

Earlier quoted context omitted.

Yeah, of course Anthropic making the version publicly available AFTER people notice it wasn't public, completely solves the issue ;)

Anthropic changed nothing since I wrote published this post a few hours ago - I updated my post to mention Bun canary since it was a point of confusion here on Hacker News.

Claude Code has shipped Bun 1.4. already more than month ago: https://github.com/anthropics/claude-code/releases?q=bun&exp...

Version was changed in Bun in May 18

https://github.com/oven-sh/bun/commit/b18bf6d1d0a92238f240bf...

So it has been canary since then, most likely, if docs are accurate that latest main is canary.

Re: Claude Code uses Bun written in Rust now

#143

Post by simonw »

alexandra_au wrote: post #89
feverzsj wrote: post #65

It's a transpile. And not even a good one. The generated code is far from idiomatic rust. Some may consider it an abomination.

grep -nr 'unsafe' . Is all you need to know to consider how much of an abomination it is

This comment inspired me to take a look at the trend of "unsafe" in the Bun code over time since the rewrite PR first landed - here are the commits where that number changed by at least 10:

  2026-05-14 23427db 13907
  2026-05-14 19d8ade 13861
  2026-05-15 4d443e5 13840
  2026-05-17 172afa5 13803
  2026-05-17 80a06a8 13849
  2026-05-18 fba43af 14026
  2026-05-19 303cd28 14052
  2026-05-20 21db682 14243
  2026-05-22 a06a00a 14239
  2026-05-23 49c97de 14090
  2026-05-28 472a06a 14076
  2026-06-01 a0d1472 14071
  2026-06-04 8553428 14032
  2026-06-09 717542f 14053
  2026-06-10 1c90e5a 14043
  2026-06-11 6e91d24 14031
  2026-06-16 bd8edc7 14086
  2026-06-17 6ef5977 14104
  2026-06-20 315ed50 14106
  2026-06-22 c6be834 14120
  2026-06-23 ea7e44f 14108
  2026-06-23 03042ab 14128
  2026-06-29 86d32c8 14046
  2026-07-01 6640fcf 14077
  2026-07-04 51074e3 14099
  2026-07-06 9d0e93d 14186
  2026-07-08 ab6eb2d 13953
  2026-07-09 86caf6e 13936
  2026-07-10 91675d0 13930
  2026-07-13 73b6c14 13951
  2026-07-16 4bbe075 13978
  2026-07-16 57e30a5 13995
So not as much cleanup as I had expected!

ChatGPT written script for counting here: https://gist.github.com/simonw/b1015bcadcedd1a781cedb7af9cbb...

Re: Claude Code uses Bun written in Rust now

#148

Post by rvz »

softwaredoug wrote: post #137
witx wrote: post #98

What is the actual contribution and motivation of this post?

People shouldn’t overthink blog posts. Just write what’s on your mind and have fun.

The motivation is obviously clear. No-one would be doing that for fun 24/7, only covering about AI and nothing else without getting paid for it.

If anyone else did that on HN, they would be accused of slop with their domain blacklisted.

Re: Claude Code uses Bun written in Rust now

#149

Post by jqbd »

rs_rs_rs_rs_rs wrote: post #58

It is absolutely amazing to me that this ai rewrite work so well, maybe claude is not really that much of a complicated tool to stress the bun runtime but still...

It works well because they had tests, they could compare before and after. Likelihood of issues especially if you transpile to a safer language should be minimal.

Re: Claude Code uses Bun written in Rust now

#150

Post by nicce »

zarzavat wrote: post #90
conartist6 wrote: post #76

Earlier quoted context omitted.

Haha TS7 is the next biggest example of, "Let's just do a line by line port to another language instead of seriously examining our architecture"

Indeed as much I dislike the approach Bun took, at least the port appears to be working. TS7 is going to cause problems for downstream users because Go is the wrong language to use for something that has to run in WASM.

> TS7 is going to cause problems for downstream users because Go is the wrong language to use for something that has to run in WASM.

Is there a huge need to run that typechecking on browsers?

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