Anthropic redesigns source code management

To cope with the surge in merges caused by AI agents writing code, Anthropic built an in-house version control system, Scion, and fully migrated its monorepo from git within five months. Its average daily merged code changes rose from about 2,500 in May 2026 to over 30,000 in September. Scion assumes clients are always online, with asymmetric client-server design; clients keep only a bounded object cache and use sparse and virtualized checkouts. Anthropic says its infrastructure's CPU and memory footprint is 200 times smaller than the previous git mirror approach, CI checkouts dropped from minutes to seconds, and CI alone gained a 25% CPU capacity benefit. The system was designed from the start to support repository-level access control and directory-level permissions, to protect sensitive code while retaining monorepo advantages. The team of seven built both Scion and the code review tool Antique.