Summary & Key Takeaways ​

• Bun's core has been rewritten from Zig to Rust due to persistent memory management bugs.
• Rust's memory safety features were a primary driver for the language switch.
• The rewrite was largely facilitated by advanced AI agents (Mythos/Fable).
• Bun's existing TypeScript test suite served as a crucial conformance suite for the AI-driven port.
• This project challenges the long-held "never rewrite" adage in software development.
• The AI agents performed dynamic workflows, trial runs, and adversarial review.
• The initial experiment with AI agents quickly yielded a high percentage of passing tests.

Our Commentary ​

This is wild. I genuinely don't know how to feel about agents churning away at 3am while nobody's watching, rewriting a core runtime. It's a massive technical feat, sure, but also a bit unsettling. We've always said "never rewrite," and now AI just... does it? The implications for DX and project longevity are immense, but I'm still processing the "how."