GoKawiilMicrosoft rewrites GitHub Copilot's runtime from TypeScript to Rust using AI agents
Microsoft used AI agents to convert the Copilot runtime's 430,000 lines of TypeScript into 800,000 lines of Rust, a project that took about 14.5 weeks, over 135 releases, roughly $120,000 in AI token costs, and three weeks of human developer oversight to fix dozens of regressions. The Rust version now powers Copilot across VS Code, Visual Studio, the CLI, SDK, and Office apps like Excel and Outlook.
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The rewrite delivered nearly 16x faster session throughput and over 10x lower memory use, showing tangible performance gains from moving core AI infrastructure off TypeScript. It also serves as a real-world case study on the current limits of AI-driven code migration, since human engineers still had to catch and fix numerous bugs the agents introduced.
- AI agents ported 430,000 lines of TypeScript to 800,000 lines of Rust for about $120,000 and three weeks of human effort.
- The Rust runtime is roughly 16x faster and uses about 10x less memory than the original TypeScript version.
- Despite automation, dozens of regressions required manual fixes, highlighting AI's current struggles with Rust's complexity.
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Published there as: “Microsoft agentically ports Copilot runtime to Rust for $120K”
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