Anthropic builds custom Scion version control system to support AI-driven code surge

Anthropic has developed a custom version control system called Scion to handle a massive surge in code production driven by its AI agent, Claude. Between May and September 2026, the company’s daily code merges increased tenfold, rising from approximately 2,500 to over 30,000. Reports indicate that Claude is responsible for more than 80% of Anthropic’s merged production code.

The rapid pace of AI-driven development created significant bottlenecks for traditional Git-based workflows. Anthropic’s monorepo reached nearly 100GB in history, and the continuous integration (CI) system required approximately 25 million code checkouts daily. To address these constraints, a team of seven engineers spent five months building Scion, which utilizes a client-server architecture that moves heavy operations like commits and merges to the server side.

In addition to Scion, Anthropic implemented a code review system named Antique. The migration to Scion has reportedly improved efficiency, reducing CPU and memory usage to about 1/200 of the previous Git mirror solution and increasing code checkout speeds for CI and research tasks by two orders of magnitude.