AI broke Joel Spolsky's rewrite rule: Microsoft's Toub rewrote Copilot's 400k-line runtime in Rust alone
msharmas · x · 2026-11-03
ryanlpeterman revisits Joel Spolsky's famous 2000 essay "Things You Should Never Do," which called rewriting from scratch the worst strategic mistake in software — and argues AI has collapsed the cost of writing code, changing the math entirely:
- Anthropic's Jarred Sumner rewrote Bun in Rust in 11 days, with major performance and correctness gains.
- Microsoft Distinguished Engineer Stephen Toub single-handedly rewrote GitHub Copilot's 400,000-line runtime in Rust.
The author interviewed Toub about how and why he did it; the episode covers his Rust choice, the rewrite process, and lessons learned.
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