The Jacobian conjecture — proposed by Ott-Heinrich Keller in 1939 and listed as Smale's 16th problem — asked whether every polynomial map from complex n-space to itself with constant nonzero Jacobian determinant is invertible. Claude Fable 5's counterexample proves the answer is no. This is among the most significant mathematical results produced by an AI agent — not an incremental improvement or pattern recognition, but a definitive disproof of a conjecture that resisted human mathematicians for 87 years. Wikipedia's rapid update suggests the mathematical community has already validated the result.