Claude Fable 5.1 decoded a centuries-old royalist message hidden in plain sight since 1653
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Anthropic's Claude Fable 5.1 reportedly solved the 'Cyphral Distich,' a numerical puzzle by Sir Thomas Urquhart published in 1653, which researchers had considered unsolved. According to Vals AI, the model cracked it in 44 minutes without human assistance, after other frontier models had failed to produce a verifiable solution on similar unsolved puzzles. Fable 5.1 was tasked with finding a solvable puzzle on its own and flagged this one as promising. The key involved using each number to point to a word in one of 32 sections of Urquhart's publication, where the first letters spelled a royalist message supporting King Charles II. The solution appears simple in hindsight and humans could have solved it, but Fable 5.1 succeeded through systematic trial and error and persistence rather than advanced cryptanalysis.
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