Microsoft's AI agents rewrote 430,000 lines of Copilot code. The tokens cost $120,000.
Microsoft used AI agents to port the GitHub Copilot runtime from TypeScript to Rust, module by module, over 14.5 weeks, The Register reported.
The bill was about $120,000 in token usage, plus roughly three weeks of developer time. The agents turned 430,000 lines of TypeScript into 800,000 lines of production Rust. They opened around 1.3 port pull requests a day across more than 135 releases, using GPT-5.6 Sol and Claude Opus 4.8.
Microsoft reports the rewritten runtime runs 15.9 times faster on its benchmark, rising from 7.55 to 120 lifecycles per second. Memory for a ten-client batch fell from 1,383 MB to 126 MB.
Stephen Toub, a Microsoft distinguished engineer, wrote that this is "in no way a claim that every large TypeScript program should become Rust", and that the idea "if it compiles, it's correct" is useful "only as a joke". Dozens of regressions came from ambiguous semantics and missing features no compiler could catch.
At RustConf, consultant Lisa Crossman said: "Rust stops the agent writing memory unsafe code; it does not stop the agent writing the wrong program correctly."
Which of your migrations is still quoted in consultant months when somebody could now quote it in tokens?
Sources
Our file on Microsoft
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For your next steering committee
- 1Ask which AI tools already touch your ERP or finance data, including the ones nobody approved.
- 2Ask what each tool is allowed to change, and who reviews what it changed.
- 3Ask how the result is measured, and who decides to switch a tool off.
Issue 01 of the ERP LEADERS brief puts a timeline, the three-number review and six questions on one page. Read issue 01
Welcome back. · Issue 01