Microsoft agentically ports Copilot runtime to Rust for $120K

The software engine underpinning GitHub Copilot and a growing number of Microsoft products is now written entirely in Rust, with AI agents doing most of the porting work. The migration cost about $120,000 in AI token usage plus about three weeks of a developer's time. However, managers also had to grapple with a few dozen regressions in the resulting code, pointing to AI’s ongoing challenges in understanding Rust. The effort updated the runtime module-by-module until the job was completed, spanning over 135 releases across a 14.5-week time period. Roughly 1.3 port pull requests were opened per day. Overall, agents converted 430,000 lines of TypeScript into 800,000 lines of production Rust. To keep the port as simple as possible, the port...

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