Github ported the copilot runtime to 800k lines of rust and says the rewrite wasn't affordable…
github ported the copilot runtime to 800k lines of rust and says the rewrite wasn't affordable before agents. the tool just became its own migration tool.
next decade's rewrites get priced in agent-hours, not engineer-years.
Context
GitHub's post of 16 September 2026 says the runtime behind Copilot CLI, the app and the SDK was rewritten from TypeScript, Node and V8 into more than 800,000 lines of production Rust, mostly written by AI agents across 128 pull requests and shipped incrementally, and says a rewrite this size was not affordable before agents. It frames Rust as a choice for C ABI embedding, low overhead and predictable resource use, not a claim that every TypeScript program should be Rust.
The 800,000 is the final Rust production line count. The post's other figures are the author's estimates and are not like-for-like: about 430,000 lines of TypeScript passed through the port, and about 1,200,000 production Rust lines entered during the port while about 365,000 left. The Register, dated 18 September 2026, reports about 120,000 dollars in token usage plus about three weeks of developer time; that figure was not found in GitHub's text read, so it is unverified first-party. Next decade's rewrites being priced in agent-hours is the author's opinion.
Related work
Watch next
- GitHub follow-ups with cost data.
Sources
Provenance
The note above is reproduced unedited from the original post, first published on Threads on 18 September 2026 at 03:47 IST. Sources are the papers and datasets the note draws on.
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