A 370-Year-Old Unsolved Cipher, Solved by AI in Just 44 Minutes?

Imagine you discovered a secret message left behind 370 years ago. However, this message is filled with complex numbers that seem impossible to solve. Countless experts have tried, but for centuries, its contents remained a mystery.

Recently, however, this long-standing riddle was solved in just 44 minutes. The protagonist isn’t a human, but ‘Claude Fable 5.1,’ a new AI model recently introduced by Anthropic. Source 3

Why does this matter?

This event shows that AI is evolving into an ‘intelligent solver’ capable of cracking logical challenges that have stumped humans for centuries, moving beyond its role as a tool for writing text or generating images.

We often think of AI as little more than a ‘fluent doll,’ but this case proves how sophisticated AI’s ability to search vast amounts of data and discover complex rules on its own has become. In the future, this AI technology is expected to play a larger role in various areas of our lives, from medical research to efficient data analysis, beyond just cryptography. Source 6

Understanding it simply

This riddle, known as the ‘Cyphral Distich’ (a cipher consisting of 64 numbers left behind by 17th-century Scottish author Thomas Urquhart), first appeared in 1653. Source 1 Simply put, this cipher is composed of two lines of 32 numbers each, totaling 64 puzzle pieces. Source 12

Metaphorically, it’s like putting together a giant puzzle box with tens of thousands of pieces without an instruction manual. Humans tire easily, and checking every possible combination takes an enormous amount of time.

AI is different. Claude Fable 5.1, which performed this feat, processed 176,000 ‘tokens’ (data units AI uses to understand sentences) in an instant. Source 2 It tirelessly tested tens of thousands of rules to find the correct answer. Renowned cryptographer Bruce Schneier noted that the AI demonstrated overwhelming efficiency compared to humans in searching through and testing vast amounts of information. Source 6

Where do we stand?

So, what was the answer found by Claude Fable 5.1? Hidden behind the numbers that had been shrouded in mystery for centuries was a ‘prayer by Royalists for King Charles II.’ Source 7

This decryption result was verified by Vals AI, a company specializing in AI evaluation. Source 13 People had spent over 370 years trying to solve this problem, but in the end, cutting-edge AI technology provided the final answer. Source 5 While AI does not know everything, this clearly demonstrated its powerful performance in areas where specific rules exist or where combinations of data are crucial.

What comes next?

Through this case, we have learned that AI can be a ‘key to reinterpreting historical records.’ The domain of AI will continue to expand, from centuries-old documents and undeciphered ancient languages to complex modern data analysis.

The everyday problems you are curious about today may soon find solutions in this same way. A day is coming when AI will find and hand over treasures we haven’t yet discovered in the vast ocean of data. Aren’t you excited to see what ancient secrets AI will uncover next?

MindTickleBytes AI Reporter’s View

This achievement demonstrates that AI is becoming a powerful tool not just for generating data, but also in the realm of the ‘detective’—exploring vast search spaces and solving logical puzzles.

References

1. Claude Fable 5.1 Solves the Cyphral Distich, https://www.vals.ai/blogs/fable-solves-cyphral-distich
2. Claude Fable 5.1 Decrypts 370-Year-Old Cyphral Distich Mystery, https://securityonline.info/claude-fable-decrypts-cyphral-distich/
3. Claude Fable 5.1 Cracked a 373‑Year‑Old Unsolvable Cipher in Just 44 Minutes, https://vgtimes.com/tech-and-hardware/166170-claude-fable-5.1-在仅仅-44-分钟内破解了一个-373-年未解的密码.html
4. Claude Fable 5.1 solves a 370-year-old cipher in a Vals AI test • It Does What Now?, https://itdoeswhatnow.com/m/2026-08-31-claude-fable-5-1-solves-a-370-year-old-cipher/

5. Anthropic’s Claude Fable 5.1 Deciphers 17th-Century Cryptogram

   ForkLog, https://forklog.com/en/anthropics-claude-fable-5-1-deciphers-17th-century-cryptogram/

6. Claude Fable Solves a Historical Cipher - Schneier on Security, https://www.schneier.com/blog/archives/2026/09/claude-fable-solves-a-historical-cipher.html
7. Claude’s Fable 5.1 model cracked the code that cryptographers had been trying to crack since 1653 in 44 minutes. - Aroged, https://www.aroged.com/2026/09/02/claudes-fable-5-1-model-cracked-the-code-that-cryptographers-had-been-trying-to-crack-since-1653-in-44-minutes/
8. Fable5.1за 44 минуты разгадал шифр, над которым ученые…, https://dzen.ru/a/apfCcspJF0LmIYuL
9. Fable5.1разгадала шифр 17 века, с которым не могли справиться…, https://t-j.ru/fable51-genius/
10. GetClaudeFable5.1For Free (3 Methods) - YouTube, https://www.youtube.com/watch?v=3N9mRMb0sGs
11. ClaudeFable5.1разгадала многовековой шифр, https://kod.ru/claude-fable-rashifrovala-370-letnii-shifr

12. ClaudeDeciphers 17th-CenturyCipherText

    Crazy Alchemist, https://www.crazyalchemist.com/news/claude-deciphers-17th-century-ciphers-in-urquhart-s-treatises/

13. Anthropic’s AIsolves373-year-oldcipherin 44 minutes - el.kz, https://el.kz/en/anthropics-ai-solves-373-year-old-cipher-in-44-minutes_400052335/
14. ClaudeFable5.1Cracked In 44 Minutes ACipherThat Beat…, https://yellow.com/news/claude-fable-5-1-cracked-cipher