Claude Code uses Bun written in Rust now
Simon Willison1w4 min read
In Rewriting Bun in Rust Jarred Sumner made the following claim: Claude Code v2.1.181 (released June 17th) and later use the Rust port of Bun. Startup got 10% faster on Linux but otherwise, barely anyone noticed. Boring is good. I decided to have a poke at my own Claude Code installation to see if I could find evidence that it was using Bun written in Rust. I found these two commands convincing: strings ~/.local/bin/claude | grep -m1 'Bun v1' For me this outputs Bun v1.4.0 (macOS arm64) . The most recent release of Bun on GitHub is currently v1.3.14 from May 12th, so that v1.4.0 version number