Claude Code now ships with Bun rewritten in Rust

Claude Code uses Bun written in Rust now

Simon Willison confirmed Jarred Sumner's claim that Claude Code v2.1.181+ bundles Bun's Rust rewrite. He extracted 'Bun v1.4.0' and 563 .rs filenames from the Claude binary, proving the unreleased Rust port is already running on millions of devices. Linux startup got 10% faster; other platforms barely noticed. Sumner: 'Boring is good.'

Why it matters: Simon Willison hands-on verified Jarred Sumner's claim by extracting evidence of Rust-based Bun from the Claude Code binary, including a version number ahead of public releases. Concrete commands and outputs make it information-dense, but it's toolchain internals that don't di...