Anthropic formalizes Fermat's Last Theorem in Lean: 13.4M lines, largest proof ever
AlexKontorovich · x · 2026-09-05
Anthropic announced that one of its internal models, using the prove2.me platform, has formalized a complete proof of Fermat's Last Theorem in Lean — the final item on Freek Wiedijk's famous list of 100 formalization challenges, closing out the 20-year-old benchmark.
Key facts:
- Over 13.4 million lines of Lean code and 29,500 intermediate theorems — called "the largest Lean proof ever constructed"
- It follows the Darmon–Diamond–Taylor (1995) exposition of the Wiles–Taylor–Wiles argument, via the Langlands–Tunnell theorem and Ribet's level-lowering theorem, not the modern proof route
- The repo develops Fontaine theory and enough of Mazur's Eisenstein ideal work; combined with prior formalization of odd regular primes, the result holds fully
- Mathematician Kevin Buzzard verified the code: it compiles and passes comparator checks, taking 20x longer to compile than mathlib on a 96-core machine
A landmark moment for AI in formal mathematics.
Related event: Claude Produces First Formalized Proof of Fermat's Last Theorem in 11 Days(52 posts)→
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