A model cracks a 370-year-old cipher by realizing the key was the book itself

Claim

Handed only the instruction to solve an unsolved cipher, Claude Fable 5.1 cracked Thomas Urquhart's 370-year-old Cyphral Distich in 44 minutes by realizing the key was the book itself, each number indexing a word in one of his 32 tracts, revealing a Royalist prayer.

Reported metric: 370 years / 44 minutes

Reporting date: 2026-09-15 (not necessarily the event date)

Sources

Attribution and reporting linked by this record; links do not imply independent verification.

• Welcome to September 15, 2026 (theinnermostloop.substack.com)