Anthropic has explained why it stopped using Git and built Scion, an in-house version control system, migrating its entire monorepo in five months. In a post published on October 13, 2026, the company said its merge rate grew more than tenfold in a matter of months: from around 2,500 code changes merged per day in May 2026 to over 30,000 per day by September.
The reason is simple enough. Claude now writes so much of Anthropic's code that human-scale developer infrastructure — source control, builds and CI — has become the bottleneck, not coding itself. Scion is the company's answer, and the engineering behind it says as much about how AI agents work as it does about version control.
Why Git stopped fitting Anthropic's workload
Git is decentralized by design: every clone is a complete repository that can compute diffs, read history and check out revisions fully offline. For most projects that is exactly right, and it explains why Git became the standard. Anthropic's monorepo, however, has drifted far outside that design space.
The company says the history of its main branch alone is nearly 100 GB, while a compressed working copy exceeds 25 GB. It performs on the order of 25 million code checkouts per day for CI alone — before developer environments, agent sandboxes and research jobs. Fetched naively, that would mean over 600 PB of Git traffic per day.
- Main branch history: almost 100 GB
- Compressed working copy: over 25 GB
- Around 25 million code checkouts per day for CI
