How Anthropic ships the #1 LLM in the World safely: Separating the Brain from the Hands
Anthropic separates model 'brain' from agent 'hands' to ship frontier models safely at scale
Anthropic engineers Katelyn Lesse and Angela Jiang detail the platform architecture behind Claude, including the launch of Opus 5.5 and a design principle of decoupling the model's reasoning ('brain') from its action execution ('hands'). This separation enables safer managed agents by isolating credentials, sandboxes, and network controls from the core model. The discussion also covers scaling the Messages API (rebuilt in Rust), long-running agent harnesses, and how Anthropic manages the tension between safety classifiers and model routing in production.