Anthropic says it has replaced git inside its monorepo with Scion, a version control system it built in-house. In an engineering post published on 13 October, the company said it merged around 2,500 code changes per day in May 2026 and more than 30,000 per day by September. Coding was no longer the bottleneck. Source control, builds and CI were, because those systems were designed for human scale rather than agent scale.
Scion drops git's assumption that every clone is a complete, offline repository. Clients are expected to be online, so the server answers questions about file history and blame, creates commits and performs merges and rebases, while the client keeps a bounded local cache and fetches data on demand. Work is modelled as changesets instead of commits, spread across a distributed server tier where no single machine holds a fully materialised copy. Anthropic reports cache hit rates above 99%, an infrastructure footprint 200x smaller than its previous git mirroring setup in CPU and memory terms, checkouts in seconds rather than minutes, and a 25% CPU capacity win in CI alone.
A team of seven built Scion and its companion code review surface Antique, along with code search, source control IAM and large scale merge tooling, then migrated the monorepo in five months. Anthropic is explicit that Scion is not a general purpose drop-in replacement for git, and that shipping it for other organisations would be hard. Instead it wants to share an early view of how agentic development stresses developer infrastructure, and to work with GitHub, GitLab and the open source community on the problem.