Anthropic AI formalized the proof of Fermat's Last Theorem

Anthropic announced that its AI translated the proof of Fermat's Last Theorem into computer-checkable Lean code in 11 days: 13 million lines and 30,300 theorems.

Compiled by Sergey KostenchukPublished 2026-09-08Updated 2026-09-18

2026-09-08 Research Anthropic

🤖 Anthropic: AI formalized the proof of Fermat's Last Theorem

Anthropic (the developer of Claude) announced that its model translated the classic proof of the theorem into computer-checkable Lean code: 13 million lines, 30,300 theorems, about 6 billion output tokens, 11 days.

🌍 This is the first fully computer-checked proof of Fermat's Last Theorem: Lean independently verifies each step. The August 18 run on the Prove2Me platform used a multi-agent framework based on Claude Code with the participation of Tianyi Peng's team from Columbia University; the model is comparable in class to Claude Fable 5.1.

👤 This is a documented case: Anthropic published a research post, a technical article, and the full proof — you can verify what LLMs can really do in formal mathematics.

Source 1: https://www.nature.com/articles/d41586-026-02822-9 Source 2: https://www.anthropic.com/research/formalizing-fermats-last-theorem

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