Microsoft has used AI agents to port the runtime powering GitHub Copilot and other products from TypeScript to Rust, at a reported cost of about $120,000 in AI usage and three weeks of developer time. The migration matters because Rust substantially improved performance and reduced memory consumption, while demonstrating that agent-led software development can tackle projects that would otherwise take years.

The 14.5-week effort involved more than 135 releases, about 430,000 lines of TypeScript and 800,000 lines of production Rust, although several dozen regressions required attention. In one benchmark, Rust completed 120 session lifecycles per second compared with 7.55 for TypeScript, while memory usage fell from 1,383MB to 126MB for a comparable workload. Microsoft said the approach was tailored to requirements such as low start-up overhead, predictable resource use and C-ABI embedding, rather than suggesting every large TypeScript project should be rewritten.