What the post says
Anthropic's source control team replaced git for the company's monorepo. In May 2026, Anthropic merged about 2,500 changes a day. By September, it merged more than 30,000 a day. CI checks out code about 25 million times a day. A compressed working copy is over 25 GB. Fetch a full copy each time and that is about 625 PB a day, by our estimate.
A team of seven built a new system, Scion, and moved the monorepo to it in five months. The server makes the commits and answers history questions, such as who last changed a line. Many jobs need no local copy at all.
Why it matters
Git assumes that each client works offline with a full copy. Nearly all of Anthropic's clients are agents and jobs, and they are always online. Drop the offline assumption and much of the design changes. The post reports a footprint 200 times smaller than the old git mirrors, in CPU and memory.
Our take
The lesson is not to leave git. The authors say so:
Scion is by no means a suitable replacement for git for general use.
The lesson is to find where agents break a tool built for human speed. The post names builds and CI as the same kind of bottleneck.
Scion's engineers rate Claude as better than them at writing code. But often their job was to tell Claude "no" when it broke a core rule of the system. Review moved from each line to the intent of each change.
These numbers are Anthropic's own reports. We cannot check them. Read the original for the design: Redesigning source control at Anthropic, by Nick G. and the source control team (October 13, 2026).