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# Fable 5.1 cracks a 370-year-old cipher in 44 minutes
- URL: https://globalfeed.ai/en/fable-5-1-cracks-a-370-year-old-cipher-in-44-minutes/
- Published: 2026-09-14T16:30:21.000Z
- Updated: 2026-09-14T16:30:21.000Z
- Description: Vals AI reports that Claude Fable 5.1 solved Thomas Urquhart's Cyphral Distich, an encrypted verse that had resisted readers for centuries.
- Author: GlobalFeed Editor
- Tags: Fable 5.1, Anthropic, cryptography, x-AnthropicAI, dil-en, denetim-gerekli, video

In an experiment published by Vals AI, Claude Fable 5.1 was given a single open task: solve an unsolved historical cipher. The write-up says the model cracked Sir Thomas Urquhart's **Cyphral Distich** in 44 minutes, using 176k tokens and with no interjections from the author.

The cryptogram sits at the end of Urquhart's *Logopandecteision* (1653): two lines of 32 numbers each, 64 numbers in total. It was posed as an open problem in *Notes and Queries* in 1899, resurfaced in 20th-century cryptography literature, and appeared on cipher historian Klaus Schmeh's list of the top 50 unsolved encrypted messages. Frequency analysis, substitution and homophonic substitution had all failed.

## The key was the book itself

According to the post, the model latched onto two things. The cryptogram is printed right after Urquhart's 32 Proquiritations, and Urquhart makes a point of stressing that number. The poem attached to the cipher also promises an honest reader "his own heart's wishes, and the Author's minde", while the Proquiritations end with phrases like "is the desire", "wish" or "hope of".

The rule turned out to be simple: for the i-th number in a cipher line, go to the i-th Proquiritation, treat the number as a word index, and take that word's first letter. The result is a Royalist prayer: "O GOD UPHOLD KING CHARLS THE SECOND AND MAKE HIM THE SUPREME RULER OF THIS LAND". Each line holds exactly 32 letters and the lines end on "and" and "land", matching the promised rhyming distich.

Using the same method, the model also deciphered Urquhart's Cyphral Octastich from *The Jewel* (1652), which runs to 285 numbers. The author says no other frontier model he tried over several months produced a verified solve, and that he steered the model away from the hardest targets such as Kryptos K4\. His own reading: this was no feat of cryptanalysis, the clue was simple, and persistence did the work.

Full details are in the [Vals AI post](https://www.vals.ai/blogs/fable-solves-cyphral-distich?ref=globalfeed.ai).