Microsoft just paid $120k in tokens for the most documented ai migration yet. agents turned 430k…
microsoft just paid $120k in tokens for the most documented ai migration yet. agents turned 430k lines of typescript into 800k lines of rust across 135 releases, 15.9x faster with 90% less memory, and most of that time went to investigation, not code.
toub's note: the image of ai spewing code is almost the opposite.
Context
GitHub's engineering post says it rewrote the Copilot runtime into more than 800,000 lines of production Rust using the Copilot app and CLI, with agents writing most of the code, across 128 pull requests that shipped incrementally. It estimates about 430,000 lines of production TypeScript passed through the port, and reports 135 public CLI releases over the period.
The post says the agents spent far more time gathering evidence than changing code, with 10x as much exploration as mutation, and that the prompt cache hit rate was 96.22%.
A secondary write-up says the port cost about $120,000 in token usage plus about three weeks of a developer's time, that one in-process benchmark was 15.9x faster (120 against 7.55 lifecycles per second), and that a 10-client batch used 1,383 MB under TypeScript and 126 MB under Rust. It attributes the account to Stephen Toub.
The 430k and 800k line figures, the 135 releases and the evidence-gathering finding match GitHub's post. The $120,000, the 15.9x speedup and the memory figures came from the secondary write-up and were not seen in GitHub's page, so treat them as reported.
The 15.9x and the 90% lower memory are each for one benchmark, a lifecycle workload and a 10-client batch, so they do not describe the whole runtime. 126 MB against 1,383 MB is about 91% less, which fits the note's 90%.
The note says Microsoft did this. The post is from GitHub, a Microsoft subsidiary. The secondary write-up credits the account to Toub. The 'most documented ai migration yet' and the Toub paraphrase 'the image of ai spewing code is almost the opposite' are the author's, and the post's finding about exploration versus editing supports the idea.
Related work
- Migrating the GitHub Copilot runtime to Rust, using Copilot (GitHub Blog, September 16, 2026) ↗Primary source for the line counts, the pull requests, the releases and the exploration finding.
- Microsoft's Copilot Rust port cost $120K in tokens (samcodeman.com) ↗Secondary source for the $120,000 cost, the benchmark figures and Toub's name.
Watch next
- Find the original source for the $120,000 and the benchmark figures. Look for the comparison with Bun's port that the secondary write-up mentions.
Sources
Provenance
The note above is reproduced unedited from the original post, first published on Threads on 9 October 2026 at 00:34 IST. Sources are the papers and datasets the note draws on.
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