Copilot Runtime Rust Port 2026: How 832,000 Lines Got Rewritten for $120K
Microsoft’s copilot runtime rust port moved roughly 430,000 lines of production TypeScript to 832,378 lines of production Rust in about 14.5 weeks, across 128 pull requests merged continuously into main, for roughly $120,000 in attributed token spend. A single Distinguished Engineer, Stephen Toub, drove the control loop while AI agents wrote most of the code. That is the headline. The more useful story is in the mechanics: how the team kept main shippable the whole time, why a 136.3-billion-token bill landed at $120K instead of seven figures, which of the performance numbers survive scrutiny, and what the dozens of shipped-then-fixed regressions teach anyone planning an agentic migration of their own. ...