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Claude Code Has Been Shipping the Rust Port of Bun Since June 17 — Simon Willison Found 563 Rust Source Files Inside the Binary
Following Jarred Sumner's claim that Claude Code v2.1.181 and later run the Rust port of Bun, Simon Willison verified it independently on July 19 — running `strings` on the Claude binary surfaced 563 Rust source filenames, and a TypeScript preload query returned embedded Bun v1.4.0 (ahead of the v1.3.14 public release; v1.4.0 has since landed as a canary via `bun upgrade --canary`). Startup got ~10% faster on Linux and nothing else visibly changed. This is the concrete counterweight to the Zig-vs-Bun 'unreviewed slop' backlash from July 16: the most-scrutinized agentic rewrite of the year has been running in production in one of the most widely used coding agents for a month without anyone noticing.
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