Anthropic has moved its monorepo off Git onto Scion, a version control system it built in five months because Claude agents were writing more code than the existing tooling could handle. The company merged about 2,500 changes a day in May, a number that passed 30,000 by September; Scion now serves 25 million checkouts a day against close to 100 GB of main-branch history, using 200 times less CPU and memory for version storage infrastructure. Checkouts went from minutes to seconds, and CI CPU load dropped 25%. A team of seven engineers built Scion and the code review system Antique with heavy use of Claude, and they say the model now writes better code than any of them, moving their work toward architecture, constraints, and decisions.

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Redesigning source control at Anthropic