In a recent controversy, Andrew Kelley, founder of the Zig programming language, expressed anger after Bun, a high-performance JavaScript/TypeScript runtime originally written in Zig, was rewritten in Rust by its founder, Jarred Sumner. Bun was acquired by Anthropic in December last year to serve as infrastructure for its AI tools, Claude Code and Claude Agent SDK. After large-scale adoption, the Zig version of Bun encountered persistent stability issues, including memory safety bugs like use-after-free, double-free, and forgotten memory releases. In May this year, Jarred Sumner announced he rewrote Bun’s million lines of code in Rust over 11 days using Anthropic’s then-unreleased Claude Fable 5 (Mythos-level model) and Claude Code. Kelley criticized Sumner’s engineering practices, stating that even before AI became popular, Bun’s codebase was filled with hacky patches, abused assertions, and little time spent fixing bugs or technical debt.