Anthropic Replaces Git With Scion for Its Monorepo

Anthropic migrated its monorepo from Git to an internal version control system called Scion in five months, as detailed in a company engineering post. Daily merged changes rose from about 2,500 in May 2026 to more than 30,000 in September.

Scion uses an online client and server design in which the server handles commits, merges, rebases, file history, and blame. Its sparse and virtualized checkouts fetch files as needed, while distributed caches serve repository objects without maintaining a complete copy of the monorepo.

Anthropic says the Scion infrastructure footprint is 200 times smaller in CPU and memory requirements than its previous Git mirroring infrastructure. Code checkouts for research and continuous integration jobs now take seconds instead of minutes, while continuous integration gained 25% in CPU capacity. A team of seven people built Scion, the Antique code review tool and related systems and completed the migration in five months. Anthropic says Claude's ability to write code both created the bottleneck and made it possible to build the replacement quickly.