#Bun

Jarred Sumner announced the successful rewrite of the Bun JavaScript runtime from Zig to Rust, a process that took 11 days of intensive agentic engineering using Claude and cost approximately $165,000 in API tokens. This rewrite demonstrates that modern AI coding agents can make large-scale rewrites feasible, challenging the long-held 'never rewrite' wisdom. It also shows how Rust's memory safety can eliminate common bugs like use-after-free that plagued Zig's manual memory management. The Bun test suite, written in TypeScript, served as a conformance suite to validate the port. The new Rust-based Bun has been running in Claude Code since June 17, 2026, with 10% faster startup on Linux and no noticeable changes for users.