Bun’s source code rewrite from Zig to Rust was executed primarily through AI-assisted development using Anthropic’s Claude agents, specifically within a branch named claude/phase-a-port. The project creator, Jarred Sumner, merged the massive pull request (PR #30412) on May 14, 2026, which involved over 1 million lines of code added and 6,755 commits completed in roughly one week.
Claude is a model provider: they have many models. It would be interesting to learn if the models used were Sonnet, Opus, Mythos, some other internal unreleased model, or some mixture of them.
