Claude Produces First Formalized Proof of Fermat's Last Theorem in 11 Days

Anthropic announced on September 5 that Claude has completed the first full formal proof of Fermat's Last Theorem (FLT)—a project experts previously believed would take years. The achievement marks a milestone for AI in formal mathematical proof.

Confirmed

• The proof came out of an experiment initiated by Anthropic researcher Tianyi Peng, with Claude working in a nearly autonomous manner for 11 days
• Written in Lean, the proof spans more than 13 million lines of code, making it the largest formal proof ever
• It is an end-to-end, computer-verified complete proof that also establishes roughly 29,500 intermediate lemmas along the way
• Background: Fermat's Last Theorem was proposed by Fermat around 1637, and the only previous proof was given by Andrew Wiles in 1995

Why it matters

• This is the first time AI has autonomously completed a formal proof of this magnitude in frontier mathematics; the academic community had generally assumed such projects would require years of human effort
• It continues the rapid recent progress in AI-assisted formal proof research, showcasing AI's potential in verifiable mathematics

2026-09-05 ~ 2026-09-05 · 13 related posts

• [source] Claude completes first formalized proof of Fermat's Last Theorem in 13M lines of Lean — AnthropicAI · 2026-09-05
• Anthropic's Machine-Verified Fermat Proof Spans 13M+ Lines and Formalizes 29,000+ Theorems — Dr_Singularity · 2026-09-05
• Anthropic announces it has formalised Fermat's Last Theorem — Wonderful_Buffalo_32 · 2026-09-05
• [source] Anthropic model formalizes Fermat's Last Theorem in Lean in 11 days, 13.4M lines of proof — sammcallister · 2026-09-05

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