Anthropic moves its monorepo off git to Scion as merges top 30,000 a day

Anthropic built Scion, an in-house, server-side version control system, after merged code changes grew from about 2,500 to over 30,000 a day.

Anthropic has moved its entire monorepo off git and onto Scion, an in-house version control system, according to its October 13 post. The trigger was volume. Merged changes rose from about 2,500 a day in May 2026 to over 30,000 a day in September. Anthropic says the bottleneck is now infrastructure built for human scale: source control, builds and CI. If your agents are multiplying your PR volume, this is an early map of where git starts to strain.

Scion assumes clients are always online. The server answers history and blame queries and performs commits, merges and rebases. Clients keep a bounded cache and use sparse or virtualized checkouts. Anthropic says its main-branch history is almost 100 GB and that CI runs on the order of 25 million checkouts a day. Before Scion, it operated several hundred git mirrors. The Pragmatic Engineer reports that a team of seven builds and maintains the system. It also reports that Scion is written in Rust, stores data on Spanner and Cloud Storage, and is closed source. Arize relays Anthropic's claim that Scion uses 200x less CPU and memory than the mirror fleet it replaced.

You can't use Scion yourself. Anthropic says it doesn't expect many organizations to hit these problems in the near term. Daily CyberSecurity reports that Anthropic does not present Scion as a universal git replacement.

You can still borrow some of the ideas on plain git. A QWE AI Academy guide suggests a blobless clone with a cone sparse checkout for each agent job, and one git worktree per agent session. If merge queues are your pain point, Mergify offers batching and per-scope monorepo lanes. According to Flavio Copes, GitHub's stacked PRs went GA on October 6 and run through the merge queue as a single group.

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