Anthropic created Scion to replace Git in monorepositories

Anthropic has completely rewritten Git because it is too slow for AI. The company converted its monorepo from Git to its own version control system, Scion, over five months.

The main reason for the transition was agents. The number of merges into the monorepo grew from about 2,500 per day in May to more than 30,000 by September. As a result, Git became the main bottleneck in the development process.

The history of the main branch weighs nearly 100 GB, and the CI system performs about 25 million checkouts daily. Downloading the entire repository each time would generate more than 600 petabytes of traffic per day.

How Scion works

• The client is always online and downloads only the files needed for the current task
• Commits, merges, and rebases are performed on the server, so users do not need to push anything
• There is no full copy of the repository anywhere, including the server-side components
• Many CI tasks work via API without requiring standard checkouts

As a result, checkout time decreased by approximately 100 times. Infrastructure now consumes 200 times fewer CPU resources and memory. The CI system has 25 percent more computing power available.

The majority of Scion's code was written by the Claude artificial intelligence under the guidance of seven engineers at Anthropic.

Limitations of the new system

Scion's source code is not open source. Anthropic admits that this tool will not replace Git for ordinary projects. Such architecture is necessary exclusively for giant monorepos and agent swarms.