Claude Code Has Quietly Run Bun's Rust Rewrite Since June 17
Bun creator Jarred Sumner disclosed the shift; Willison verified it by pulling Rust filenames out of the binary itself.
- Jarred Sumner's Bun blog post says v2.1.181, released June 17, was the first Rust-powered build.
- The Rust port cut Linux startup time 10%; Sumner wrote barely anyone noticed the change.
- Willison's string search turned up "Bun v1.4.0 macOS arm64" and 563 embedded Rust filenames.
Why it matters: Millions ran new code for weeks before anyone announced it; a stranger's terminal confirmed what the company withheld.
Simon Willison's Weblog, citing Jarred Sumner / Bun.com blog ↗ · Jul 20, 20267/20/26