October 13, 2026
Scion: Anthropic moved off git once merges hit 30,000 a day
In four months the flow of merges at Anthropic grew from 2,500 to 30,000 a day, and git couldn't keep up with that pace.
Anthropic
@anthropicai
New on our engineering blog: how we built our own version control system. In May we merged about 2,500 code changes a day. In September, more than 30,000 a day. That pushed us up against our developer infrastructure, which was built for human scale, not for agents. Here's how we built a new version control system in five months and fully migrated our monorepo onto it from git: https://www.anthropic.com/engineering/redesigning-source-control
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Anthropic's monorepo serves 25 million code checkouts a day for CI alone. Done the usual git way, that would be more than 600 PB of traffic per day.
Anthropic built its developer infrastructure for human speed, but its code is now written by agents. Seven engineers spent five months building their own version control system, Scion, and a review surface, Antique, then moved the entire monorepo onto them from git.
The math is simple. In May 2026 the company merged about 2,500 code changes a day; by September it was more than 30,000. The monorepo carries almost 100 GB of history and more than 25 GB of compressed working copy.
The old setup relied on git mirrors: at peak, several hundred were running inside the company. Scion needs 200 times less CPU and memory. CI and research jobs fetch code in seconds instead of minutes, and in CI this freed up 25% of CPU capacity.
Scion doesn't work like git. Commits happen on the server, no full copy of the repository exists anywhere, and there is nothing to push. The system offers no git-compatible interface, only its own protocols and RPCs: code is cached by a daemon on each node and by a regional cache with a hit rate above 99%.
The team first wrote the git-to-Scion migration by hand, then handed it to Claude. With no extra instructions, it produced a version that uses 20 times less memory and runs 4 times faster. According to the team, Claude usually resolves conflicts faster than people can notice them.
You can't install it. Anthropic says plainly that Scion is not a general-purpose replacement for git and would be hard to release in a useful form. Instead of the code, the company published its principles. A git server doesn't have to work like a git client, platforms can offer server-side RPCs, and git's transfer protocol and sparse/shallow mechanics can be reworked so they don't conflict with each other.
The team posed the open question itself: what does CI mean when hundreds or thousands of changes get merged during a single test run?