Redesigning source control at Anthropic
Redesigning source control at Anthropic Interesting piece from Anthropic describing why and how they built their own custom alternative to Git, based on the dramatic increase in rate of changes to their code after the past six months.
Anthropic redesigned their source control system to address the challenges of managing a rapidly growing codebase, leading to the development of a custom system called Scion.
What happened
Anthropic faced a significant increase in code changes, prompting them to develop a custom source control system called Scion. This system was designed to handle the scale and speed of their development process, replacing Git.
Why it matters
The article highlights the challenges of managing large-scale codebases and the need for efficient source control systems. It provides insights into how companies like Anthropic adapt their infrastructure to support rapid development and AI integration.
- Custom source control systems are essential for managing rapidly growing codebases.
- Scion's centralized approach is better suited for handling large-scale development and CI workflows.
- AI integration in code review processes can be effective but requires human oversight to avoid over-engineering.
- Scion's design reflects the unique needs of AI development, including high-speed code changes and adversarial review.
The bigger picture
The redesign of source control at Anthropic has a significant impact on how large-scale AI development is managed, offering a scalable solution for handling massive codebases and enabling efficient collaboration and review processes.
Anthropic's redesign of source control with Scion demonstrates the need for scalable and efficient systems to support rapid AI development and large-scale code management.
Technical details
- Scion is a centralized source control system, similar to Subversion.
- The main branch history is nearly 100 GB, with a compressed working copy over 25 GB.
- Scion handles 25 million code checkouts per day for CI, leading to massive data traffic if using Git.
- Adversarial review is used extensively, with AI models like Claude and GPT being used to find flaws in code.
FAQ
Why did Anthropic redesign their source control system?
Anthropic redesigned their source control system to handle the dramatic increase in code changes, which grew from 2,500 to over 30,000 changes per day.
What is Scion?
Scion is a custom source control system developed by Anthropic, designed to handle the scale and speed of their development process, replacing Git.
What are the key features of Scion?
Scion is a centralized source control system, similar to Subversion, capable of handling 25 million code checkouts per day and managing a main branch history of nearly 100 GB.
Why does Scion lack offline support?
Scion lacks offline support because Claude, the AI model that is the heaviest user of Scion, is necessarily online, making offline support less important.
How does adversarial review play a role in Anthropic's development?
Anthropic uses adversarial review extensively, where AI models like Claude and GPT are used to find flaws in code. However, this requires skilled engineers to steer the process and avoid over-engineering.
This summary and analysis were generated with AI from the original article and may contain errors. Read the original for the full story.
Read the full story
Originally published by Simon Willison on Oct 13, 2026.
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