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In what ways does Anthropic use Bun? I know it's used as the "runtime" for Claude Code, but rather than porting a million lines of Zig to Rust, why not just port Claude Code to rust and not need to bundle a JS runtime at all? Does Anthropic use Bun otherwise? Maybe for JS execution tool calls in Claude responses?

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I’ve wondered the same. Especially because codex is written in rust.

Why not just port Claude code over.

But my guess is that maybe it doesn’t have as robust a test suite?

This might embolden them to do it…

It's extremely difficult to have a robust test suite for a TUI app like Claude Code. Hence regressions keep showing up in every update.

> But my guess is that maybe it doesn’t have as robust a test suite?

Not sure about what's going on over there, but over the last year Claude Code has gotten way better, I sure hope that they're working on a good enough test suite to avoid a crapload of regressions (and pave way for more refactoring, should they need it).

Things improved tremendously the first month after they acquired Bun. People like Jared (bun creator) worked relentlessly on the performance bottlenecks, and posted details on X as he worked through them. I remember just launching claude code used to take multiple seconds, and within a month it went down to instant.

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