Claude Fable 5.1 Solves a Centuries-Old Historical Cipher

Summary

Vals AI reports that Claude Fable 5.1 solved Sir Thomas Urquhart’s Cyphral Distich, a two-line cryptogram of 64 numbers that had resisted attempts since at least the 19th century. The model spent 44 minutes and used 176,000 tokens without human interjections. Its key insight was that the cipher appears immediately after Urquhart’s 32 Proquiritations and that the accompanying poem refers to readers finding their “wishes.” Rather than reconstructing an external cipher alphabet, Fable 5.1 treated the book as the key: for each number, it went to the correspondingly numbered Proquiritation, used the number as a word index, and took the word’s first letter. This produced “O GOD UPHOLD KING CHARLS THE SECOND AND MAKE HIM THE SUPREME RULER OF THIS LAND,” a 32-letter-per-line royalist prayer whose structure and rhyme provide strong internal checks. The article says the result fits Urquhart’s known Royalist politics. Fable 5.1 then applied an analogous page-based rule to the larger Cyphral Octastich in The Jewel (1652), which contains 285 numbers against 284 numbered pages. The reported plaintext is a royalist prayer in ottava rima, but nine letters remain unresolved. The author says 231 of 275 readable positions are exact first-occurrence hits in the EEBO-TCP text, while 44 are one to three words off for identified transcription or pagination reasons. The account also notes an apparent page shift from position 159 onward, an ambiguous “IRSH” in place of “IRISH,” and an unreadable nine-letter sequence. Confirming those positions requires a physical copy or the 1983 Jack and Lyall edition because the available TCP copy lacks the final quire. The author’s broader claim is that AI models may help solve historical and archival problems whose main bottleneck was sustained human attention. The article presents persistence and rapid recognition of a tractable clue, rather than extraordinary cryptanalytic complexity, as the central capability demonstrated.