Anthropic has transitioned from Git to a proprietary source control system named Scion. The company initiated this change after daily code merges surged from approximately 2,500 in May 2026 to over 30,000 by September 2026. This increase is attributed to the growing coding capabilities of Claude AI models.
The previous infrastructure struggled with a main branch history approaching 100 GB and tens of millions of daily checkouts. A team of seven engineers developed Scion, completing the migration of the company's monorepo in five months. The system incorporates design concepts from Google's Piper and Meta's Sapling.
Scion utilizes always-online clients and performs commits and merges on the server side. These changes reduced CI job completion times from minutes to seconds. Furthermore, the system achieves cache hit rates exceeding 99% and maintains a CPU and memory footprint 200 times smaller than the replaced Git infrastructure.
The shift to custom infrastructure presents potential challenges, including the loss of access to the Git ecosystem and the need for ongoing maintenance. Additionally, the company notes that long-term costs for the new system are more difficult to forecast compared to initial performance benchmarks.
