Jarred Sumner has detailed the transition of parts of the Bun runtime from Zig to Rust. This decision stems from persistent memory-safety challenges encountered when managing a codebase that combines manual memory handling with garbage collection.

To facilitate this migration without halting the development of new features for an entire year, the team utilized Claude. The AI assisted in a mechanical rewrite process that relied heavily on the existing test suite to ensure correctness and stability during the transition.