Anthropic reports that 1,000 agents running an early version of Claude Fable 5.2 reproduced a Lean-checked formalization of Fermat’s Last Theorem without Prove2Me or researcher steering. The team took 28.7 hours, used one-third as many output tokens, and produced a proof one-seventh the length of the earlier formalization. The toy experiment operated in an isolated sandbox with command screening and offline monitoring, so its results do not establish performance outside that controlled setup.