Anthropic moved its monorepo off Git as daily merges topped 30,000

Anthropic says its daily merged code changes rose from about 2,500 in May to more than 30,000 in September 2026. To handle that growth, it built Scion and moved its monorepo—a single repository containing many projects—off Git in five months. The company described the completed internal migration in an October 13 engineering post, rather than announcing a public Scion release.

When serving the code becomes the bottleneck

Version control manages files and their revision history. Git’s distributed design supports self-contained local repositories and offline work, but Anthropic’s workload increasingly revolved around online agents and automated jobs. The company reports roughly 25 million code checkouts a day for continuous integration (CI), which runs automated checks during development.

Partial checkouts, repository snapshots and hundreds of internal Git mirrors had bought it time. Those workarounds became harder to operate as merge volume grew. A seven-person team built Scion, the Antique code-review tool and several related systems while completing the migration.

Ask the server instead of keeping every copy

Scion’s server answers questions about file history and who changed a line, and performs commits, merges and rebases. Clients keep a limited local cache rather than a self-contained offline repository. The design assumes they can reach the server whenever needed.

A CI job that only needs a diff can request it without checking out files at all. When a job does need files on disk, Scion supports fetching selected directories or materializing files as they are accessed. Repeated jobs and agents therefore do not each need a complete local repository and its history just to do a narrow task.

Human review stays; a general Git replacement does not follow

Anthropic says Claude helped implement the infrastructure, while engineers supplied architectural judgment and enforced core constraints. They still had to reject unsuitable approaches and unnecessary complexity. The team reviews every change request, focusing on its intent rather than reading every line of code.

Scion also depends on bespoke review, search and CI systems, making it difficult to offer in a broadly useful form. Anthropic explicitly says it is not a suitable general-purpose Git replacement. Other teams do not need to migrate because of this announcement; as agent usage grows, they can examine whether fetching code, running automated checks or reviewing changes is becoming their own bottleneck.