GitHub Migrates Copilot Runtime to Rust

GitHub migrated the Copilot runtime from TypeScript and Node.js to Rust using an AI-assisted rewrite that replaced over 800,000 lines of code. The process took 14.5 weeks and involved 128 pull requests. Startup time dropped from 5.25 seconds to 292 milliseconds. By August 21, the runtime contained 832,378 lines of Rust production code and 468,689 lines of unit tests.