Claude Fable 5.1 Cracks 373-Year-Old Scottish Cipher

Scottish writer and translator Sir Thomas Urquhart published the Cyphral Distich in his 1653 book, Logopandecteision. The cryptogram consists of two rows of 32 numbers and resisted conventional approaches including frequency analysis and substitution methods for centuries. Its apparent solution matters because it offers a concrete test of whether large language models can sustain open-ended investigation, connect structural clues across a long document and generate a verifiable answer rather than merely reproduce known information.

Vals AI said on Aug. 31, 2026, that a researcher gave Anthropic’s Claude Fable 5.1 the task and provided no further intervention. The model took 44 minutes and used about 176,000 tokens to infer that each number indexed a word in the corresponding one of Urquhart’s 32 Proquiritations; the selected words’ initials revealed the plaintext. The 64-letter message asks God to uphold King Charles II and make him supreme ruler of the land, though the result remains a Vals AI-reported finding rather than an independently authenticated scholarly conclusion.