Anthropic has replaced git with Scion, its own in-house version control system, for its monorepo, the single repository that holds all its code.

As Claude's coding speed pushed daily merges from about 2,500 in May to more than 30,000 by September, source control became the company's biggest development bottleneck, so Scion was built for always-online AI agents and automated test jobs, with tasks like history and merges handled on the server. According to Anthropic, it uses about 200x less CPU and memory than the previous git setup and cuts checkout times from minutes to seconds, though Scion won't be open-sourced.