Microsoft agentically ports Copilot runtime to Rust for $120K

Microsoft successfully migrated the Copilot runtime from TypeScript to Rust using AI agents, converting 430,000 lines of code to 800,000 lines of production Rust at a cost of approximately $120,000 in AI tokens and three weeks of developer time. The Rust version achieved a 15.9x performance speedup and reduced memory consumption from 1,383 MB to 126 MB for the same workload, though the migration required addressing several dozen code regressions. The runtime now powers Copilot across multiple Microsoft products including GitHub Copilot, VS Code, Visual Studio, and Office applications.