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Source Control System

1 post · Oct 2026

What this trail covers

Anthropic has developed and migrated to Scion, a horizontally scalable, client-server source control system designed for AI-driven development workflows. Scion replaces Git for their monorepo, addressing limitations in scale and performance by assuming clients are always online, employing client-server asymmetry, and enabling scalable API access to repository data. It features server-side commits, derived data structures for efficient querying, and a sparse/virtualized checkout client. This system supports Anthropic's rapid code iteration driven by AI coding assistants.

All Anthropic trails
  1. Redesigning source control at AnthropicThis post details the design and implementation of Scion, Anthropic's in-house source control system, built to handle the extreme scale of AI-driven code generation. Key contributions include: a client-server architecture assuming online clients, client-server asymmetry where the server handles complex operations, horizontally scalable components with no fully materialized repo, cheap/incremental/lock-free server-side commits, and optional/sparse/virtualized working copies. It introduces 'changesets' as the unit of work and 'derived data' computed recursively from parent changesets for efficient querying (e.g., blame, history). The client protocol focuses on requesting specific objects (trees and blobs) recursively, enabling tiered caching and efficient, resumable operations without large packfiles.