If I had to guess, it comes down to speed of iteration. Claude Code is built on JavaScript, so Bun aligns well with their current stack.

Switching to Go or Rust would only make sense if performance were the main priority, which doesn’t seem to be the case. Their current setup lets them ship quickly. A rewrite in Go would likely slow that down.

Codex moved to Rust, and you can see the trade-off. Performance improved, but release velocity dropped. They’re also still catching up to Claude Code, so they don’t face the same pressure to ship as fast.

Claude is still better at writing JS than it is Go.

My guess: JavaScript runs in the Browser as well as on the OS. That way you can train a model to be able to interact with both fairly simple. You can also see that their harness, claude-code is also written in js. So I guess they are quite invested in that language anyway.

Yeah, it's the same pattern you saw in the early react days where open source devs would try to "woo" the react core team into getting recognition to sell consulting services or courses.

The bun people likely have some fucked up incestial business relationship with some >dev manager at Anthropic and the same pattern is repeating. Only this cycle it's going straight to acquisitions, which honestly seems like a worse strategy and Anthropic will def can the bun engineers in less than <3 years or whenever they face an actual budget crunch that they can't stave off with more gulf money.

I’m wondering why Anthropic, who has “the most powerful, hold me bro, AI in the world” just didn’t vibe code their own, better, version of bun? haven’t Dario said that coding is cooked in 6 month, like 12 months ago?

Is Claude better with Javascript than it is with Go code? Seems like it could be true.

I doubt those SWEs could have used anything other than JS.

One of them is a much more efficient but obscure programming language from a competitor, the other is what the web is built on.