Lean 4 proof of Fermat's Last Theorem: how Claude did it in 11 days
On September 4, 2026, Anthropic published a complete Lean 4 proof of Fermat's Last Theorem: 13 million lines, written largely by Claude agents in 11 days, and checked by a machine rather than by referees. The mathematician who has led the human effort to do the same thing since 2024 confirmed that it checks out, and then wrote that it tells us "essentially nothing" about mathematics. Both are…
On September 4, 2026, Anthropic unveiled a fully formalized Lean 4 proof of Fermat's Last Theorem, generated by an army of dozens of Claude agents in just 11 days. The colossal proof, spanning 13 million lines, was then meticulously verified by a machine rather than by human referees. The mathematician spearheading the human effort to achieve the same feat since 2024 confirmed the proof's validity, but admitted that it provides essentially no new insights into mathematics.
The stark contrast between the proof's impressive scale and its limited mathematical significance is what truly intrigues those who develop software requiring absolute correctness.
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