Claude formalized Fermat's Last Theorem in 11 days, writing 13M lines of Lean across 29,500 theorems

dl_weekly · x · 2026-09-13

Anthropic has shared the first complete computer-checked proof of Fermat's Last Theorem, produced by Claude working largely autonomously over 11 days in the Lean proof assistant — roughly 13 million lines of code proving 29,500 intermediate theorems. The effort was initiated by Anthropic researcher Tianyi Peng, whose group at Columbia builds AI formalization tools, to test how far Claude could push FLT formalization. Context: Wiles's original 1995 human proof ran 129 pages; a multi-year community formalization effort led by Kevin Buzzard at Imperial College began in 2024. Buzzard called the result an extraordinary autoformalization achievement, and Anthropic discusses what it could mean for research mathematics.

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