TonyBai

Sep 24, 2026 · Backend Development

One Engineer, 3 Months, 830K Lines: GitHub Rewrites Copilot Runtime in Rust with Copilot

GitHub engineer Stephen Toub details how a single engineer used Copilot to rewrite the Copilot Agent Runtime from TypeScript to Rust in 14 weeks, producing 832K lines of Rust code with 18x latency improvement and 91% memory reduction at a cost of $120k in tokens, while maintaining quality through in-place migration and rigorous testing.