GitHub rewrote the Copilot agent runtime into 800k lines of Rust, mostly written by AI agents
PaulShellDev · x · 2026-09-17
- GitHub's engineering blog details migrating the Copilot agent runtime (powering Copilot CLI, app, and SDK) from Node.js/TypeScript to over 800,000 lines of production Rust.
- Most of the code was written by AI agents across 128 PRs landed incrementally; regressions were caught and fixed quickly along the way.
- Performance improved by orders of magnitude; a project that would have taken a team 1–2 years was done primarily by a single developer in a few months.
- The SDK is now positioned as a shared Runtime/SDK across products—a landmark first-hand account of agents writing large-scale production code.
Related event: GitHub Rewrote Its Copilot Runtime in 800K Lines of Rust Using Copilot(10 posts)→
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