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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.

A second command extracting .rs file paths from the binary turns up 563 Rust source filenames, giving direct evidence that Bun's Rust codebase is compiled into the shipped tool. ✦ AI generated

Simon Willison · Simon Willison's Weblog · 2026-07-19 · original ↗

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This outputs a list of 563 filenames, starting with these: src/runtime/bake/dev_server/mod.rs src/runtime/bake/production.rs src/bundler/bundle_v2.rs

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✳ Bun ✳ Claude Code

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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.Simon Willison · Simon Willison's Weblog · conf 60%

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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 Weblog supports → 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 Weblog supports → Jared Sumner rewrote Bun's entire codebase from Zig to Rust by running 64 parallel Claude (Fable pre-release) instances across four work trees, porting and validating files against the existing test suite.Scott Tolinski · Syntax