GPT-6 Astra autonomously broke a previously unsolved Enigma message from WWII by developing its own cryptanalysis software and identifying a repeated phrase as a crib for attack. The breakthrough sparked similar successes, with Claude Opus 5 subsequently breaking another long-encrypted message using the same approach.

• GPT-6 Astra independently selected message Nr. 172 (MVUEH) as the most promising target, then built Python and C++ Enigma simulators and a Bombe implementation to crack it
• The AI identified "ROSENOW ROSENOW" as a repeated plaintext fragment and used it as a known-plaintext attack vector to recover the key
• Claude Opus 5 followed up by breaking message Nr. 205 using a signature phrase (XHARTJENSTEINX) as the crib, showing the technique's reproducibility