DataArticle
Running strings on a local Claude Code binary and grepping for 'Bun v1' reveals the string 'Bun v1.4.0 (macOS arm64)', a version number newer than any publicly released Bun build.
The author ran a strings/grep command on their own Claude Code install and found a 'Bun v1.4.0' identifier, implying Anthropic is bundling a preview of an unreleased Bun version. ✦ AI generated
Simon Willison · Simon Willison's Weblog · 2026-07-19 · original ↗
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.
Read full article ↗excerpt · fair-use quotation
Around this claim
This moment responds to
supports → The combined evidence confirms that Bun's Rust rewrite is genuinely running in production on millions of devices via Claude Code, quietly and without fanfare.Simon Willison · Simon Willison's Weblogsupports → Claude Code version 2.1.181 (released June 17th) and later versions run on the Rust port of Bun, which made startup about 10% faster on Linux, though almost nobody noticed the change.Jarred Sumner · Simon Willison's Weblogextends → A second strings/grep command against the Claude Code binary extracts a list of 563 Rust source filenames, including files like src/runtime/bake/dev_server/mod.rs and src/bundler/bundle_v2.rs, embedded in the compiled binary.Simon Willison · Simon Willison's Weblog