Intel / article

Redesigning source control at Anthropic

Source: simonwillison.net
Date: Published Oct 13, 2026

Context

Anthropic built Scion to reduce the source-control work repeated by its growing fleet of coding agents and automated jobs. The company reports that daily merged changes grew from roughly 2,500 in May to more than 30,000 in September 2026. Its replacement system lets a job request information such as a code difference directly from a server, without first maintaining a local repository. Engineering account.

When files are needed, Scion can fetch selected directories or materialize files on demand. Those choices target repeated copying and repository maintenance at enormous scale. Anthropic says the design only makes sense for enormous monorepos and is not a general replacement for Git; adopting it would also require changes across code review, search and continuous integration. Design and scope.

Key takeaways · AI-distilled

Anthropic's merged code changes rose from about 2,500 per day in May 2026 to over 30,000 per day by September, according to the article Simon Willison quotes.
Anthropic's main-branch history is almost 100 GB, a compressed working copy exceeds 25 GB, and CI runs about 25 million checkouts a day, which it says would mean over 600 PB of daily git traffic if fetched naively.
The replacement, Scion, was built by seven people and the migration off Git took five months; Willison likens it to centralized systems such as Subversion. The new code review system is called Antique.
Anthropic reports adversarial model review is effective but can be myopic, so engineers had to steer Claude away from over-engineering in response to hypothetical concerns.

Read the source simonwillison.net