Microsoft uses AI agents to port Copilot runtime to Rust

Microsoft has successfully migrated the software engine powering GitHub Copilot and various Microsoft cloud services from TypeScript to Rust. The migration was largely performed by AI agents, costing approximately $120,000 in AI token usage and requiring three weeks of developer time.

The process involved converting 430,000 lines of TypeScript into 800,000 lines of production Rust across 135 releases over a 14.5-week period. While the transition resulted in a few dozen code regressions, the performance gains were significant. Benchmarks showed a 15.9x speedup in session lifecycles compared to the original implementation. Additionally, memory consumption for a 10-client batch of agents dropped from 1,383 MB with TypeScript to just 126 MB with the Rust rewrite.

The Copilot runtime supports a wide range of tools, including the GitHub Copilot CLI, SDK, and cloud agents, as well as integrations within VS Code, Visual Studio, Excel, Outlook, and PowerPoint.