Claude Fable 5.1, an AI model, has solved the 370-year-old Cyphral Distich cipher, a cryptogram that had remained unsolved for centuries. The solution was found by using a simple rule based on the book's content, where each number in the cipher corresponds to a word index in the book. The model was able to solve the cipher in 44 minutes, and its solution has been verified. The success of the model demonstrates its ability to solve historical mysteries and forgotten conjectures.