Anthropic has stopped using Git for its main codebase. In an engineering post published today, the company says its monorepo went from about 2,500 merged changes a day in May to more than 30,000 a day by September, a surge it pins on Claude writing more and more of its code. Git couldn't keep up, so a team of seven built a replacement called Scion, plus a code review tool called Antique, and moved the whole repo over in five months.
The numbers explain why. The main branch history alone is almost 100 GB, a compressed working copy is over 25 GB, and CI checks out code around 25 million times a day. Anthropic says fetching all that naively would mean more than 600 PB of Git traffic every day, and at its peak it was running several hundred internal Git mirrors just to cope. Scion assumes every client is an agent or job that's always online, so the server handles history, blame, commits and merges, and machines only pull down the files they actually read. Anthropic says the new setup needs 200 times less CPU and memory than the old mirror fleet, checkouts take seconds instead of minutes, and CI got back 25% of its CPU capacity.
The more striking part is how it got built. Anthropic says an early snapshot of Claude Mythos Preview rewrote its hand-written ingestion pipeline with no extra instructions, and the new version used 20 times less memory while running four times faster. Every engineer on the project would now rate Claude as a better coder than themselves, and the post says that "very often, we found that the role of the engineers was to tell Claude 'no.'"
Don't expect to switch to Scion yourself. Anthropic calls it "by no means a suitable replacement for git for general use" and isn't releasing it. Instead, it wants to work with GitHub, GitLab and the open-source community to bring some of the ideas to Git, and it expects other companies leaning on AI coding tools to hit the same walls within six to 12 months.
— via Anthropic.