Scion: Anthropic is replacing Git with its own version control system, built in five months by seven people using Claude

With the number of code merges rising from 2,500 to over 30,000 per day between May and September, Anthropic migrated its monorepo from Git to Scion, an in-house tool designed for agents that are always online.

Anthropic explains on his engineering blog why git became his main bottleneck. In May 2026, the company merged about 2,500 code changes per day; in September, over 30,000. The history of the main branch of its monorepo approaches 100 GB, and the IC carries out approximately 25 million code extractions per day, which would represent more than 600 Po of daily git traffic. At the strongest, several hundred internal git mirrors rotated to absorb the load.

A tool designed for customers always connected

Finding that almost all of its "clients" are agents and tasks online, the Scion team designed principles against git: everything happens on the server side (no push), the data is distributed without a full copy of the repository, the "changesets" store only the modified files, and the extractions are partial or virtualized. Common queries (diff, blame, merge base) go through an API without a local copy. Announced result: 200 times lighter CPU and memory infrastructure than old mirrors, extractions in seconds rather than minutes and 25% CPU capacity released on the IC.

Seven people built Scion, the Ancient Code Review tool and half a dozen related systems, and then migrated the whole in five months. Anthropic explains that all these engineers now consider Claude better than they do to write code, but that their role was to impose architecture and, often, to say "no" to the agent when he circumvented the constraints of the system or over-protected the code.