Claude Code uses Bun written in Rust now
Claude Code version 2.1.181 and later use the Rust port of Bun, resulting in a 10% faster startup on Linux. The Rust version of Bun has been released as Bun canary and can be installed by running bun upgrade --canary. The use of Bun in Rust has gone largely unnoticed, with the change being described as 'boring is good'.
- ▪Claude Code version 2.1.181 and later use the Rust port of Bun.
- ▪The Rust version of Bun has been released as Bun canary.
- ▪The use of Bun in Rust has resulted in a 10% faster startup on Linux.
Opening excerpt (first ~120 words) tap to expand
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 in Claude supports them shipping a preview of a not-yet-released Bun version.
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Excerpt limited to ~120 words for fair-use compliance. The full article is at Simon Willison’s Weblog.
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