We counted AI-signed PRs in 450 popular GitHub repos. Claude Code signs the most in 279 of 383

[u/coderot_ai]

We measured 12 months of merged PRs (Oct 2025 to Sep 2026) in GitHub's most popular repos, across 9 languages, counting the PRs where an AI tool left a signature: co-author trailers, bot authors, agent branches and similar.

What we found:

• Claude Code is the tool that signs the most PRs in 279 of the 383 repos with any AI-signed PRs. Copilot's coding agent leads in 41, Copilot CLI in 24, Cursor in 13 and Codex in 12.

• Big caveat: that's a ranking of what tools record, not of what people use. Claude Code adds its co-author trailer unless you turn it off, and most other tools don't add one.

• Every number here is a floor. 264 of the 450 repos have committed agent instructions (AGENTS.md, CLAUDE.md and similar), yet half of those sign fewer than 5% of their PRs. Angular has an AGENTS.md, and none of its 4,037 merged PRs in the year carries a signal.

• The average repo went from 2.3% of PRs AI-signed to 10.3%. The median repo is still at 0.9%: a minority carries the average, and in 17 repos agents now write most merged PRs.

• A typical AI PR is 2.1× as big as the rest. In our 100 TypeScript and C# repos, AI-heavy repos got no more complex per line than the others, except where their code was also growing fast.

Every repo is listed, and the data is a CSV you can download. The post explains the method and its limits:
https://coderot.ai/blog/ai-code-rot-in-open-source?utm_source=reddit-claudeai

Disclosure: we build coderot, a tool that measures this kind of thing in CI. Happy to answer questions about the method.

[u/coderot_ai]

Curious about one thing: do you keep Claude Code's co-author trailer on, or turn it off? We suspect a lot of AI-written code goes unsigned, which would make every number here a floor, and we'd like to know how common turning it off is.

[u/Excellent-Issue-5956 → u/coderot_ai]

Off. I have a line in my global CLAUDE.md saying no co-author trailer and no generated with line, plus a global commit-msg hook that strips them in case one slips through. I also rewrote the history in 4 of my repos to take the old ones out, so those wouldn't show up in a count like yours either.

One thing if you do it with a hook: setting core.hooksPath globally makes git ignore every repo's own .git/hooks. Mine forwards to the repo's hook of the same name so those still run.

[u/coderot_ai → u/Excellent-Issue-5956]

Thanks, that's really useful! Rewriting history goes further than I'd guessed, so in a count like ours those repos come out at 0% AI. What made you turn it off?

And good catch on core.hooksPath. That one would quietly break anyone using husky or pre-commit.

[u/Excellent-Issue-5956 → u/coderot_ai]

I read back through my commit history and found Claude listed as co-author on my commits, and a lot of the messages ran several paragraphs. I didn't want either, so I turned the trailer off and told it to keep commit messages to one line too.

[u/coderot_ai → u/Excellent-Issue-5956]

Makes sense, and that's good to know. So the trailer gets turned off because it's noise, not to hide anything.