On September 4, Anthropic announced that its Claude agents had cranked out the first-ever fully computer-verified formal proof of Fermat's Last Theorem in just 11 days. The company said the project wrapped up last month. Anthropic stressed that this is a true formal proof, fully machine-verified from start to finish.

What Happened

According to Anthropic, the team used a formalization approach—basically translating mathematical reasoning into a strict format that proof assistants like Lean can check. They’re calling this the “first” complete machine-verified version of the proof for this theorem. The 11-day turnaround is specifically attributed to the Claude agents.

Why Formalization Matters

Human verification of massive math proofs can take years. Formalization speeds things up and makes the process safer, since a computer system rigorously checks every step against set logic and axioms. Anthropic highlights the value of this approach for bulletproof verification of major results.

Context

Fermat's Last Theorem is a classic number theory problem that stumped mathematicians for centuries. In its famous form, it deals with the equation aⁿ + bⁿ = cⁿ. Anthropic’s announcement isn’t about a new math discovery, but about the first time a computer has fully checked a formalized proof of the theorem end-to-end.

Dates and Details

Anthropic made the announcement on September 4, 2026, noting that the formalization was completed last month. Claude agents took 11 days to prep the formal proof version.