Anthropic replaces Git with Scion, its own source control built for agents

Anthropic says that with Claude writing so much of its code, the bottleneck is now developer infrastructure built for human scale: source control, builds and continuous integration (CI), which builds and tests every change. It merged about 2,500 code changes a day in May 2026 and more than 30,000 a day in September.

The main branch of its monorepo, the single repository that holds its code, has almost 100 GB of history, and CI checks out code about 25 million times a day. Several hundred internal Git mirrors stopped scaling, so a team of seven built Scion and Antique, a code review tool, and moved the monorepo onto them in five months.

How Scion differs from Git

Scion assumes its clients, mostly agents and automated jobs, are always online. The server handles history, blame (who last changed each line), commits, merges and rebases, and an API exposes all of it, so many jobs need no local copy. A job that needs files fetches only what it reads.

Checkouts take seconds rather than minutes, and CI alone gained 25% in CPU capacity. An early snapshot of Claude Mythos Preview rewrote the pipeline that copies Git history into Scion; its version used 20 times less memory and ran 4 times faster.

Anthropic says Scion is no general replacement for Git and would be hard for other organisations to adopt. It wants to work with GitHub, GitLab and the open source community on the same problems.