Anthropic's Scion version control system closely mirrors Meta's Mononoke design

Anthropic introduced Scion, a version control system built to handle around 30,000 daily code merges from AI agents, and presented it as an in-house solution. A former Meta engineer, Rain, observed that Scion's data model, terminology, and architecture closely resemble Mononoke, a server she helped design at Meta in 2018. Anthropic's blog credited Meta's Sapling client but did not mention Mononoke, and Rain later received private confirmation that the resemblance was intentional, citing personnel overlap with people familiar with Mononoke. The episode has prompted discussion about how AI-assisted development handles attribution, since models reproduce existing designs without citing their origins. Rain has said she objects to the removal of attribution rather than to the reuse of good ideas.