GPT-6 Astra decoded a WWI German radio cipher from November 27, 1918. The message reported an English cruiser arriving at Sevastopol on the 24th. An allied squadron followed on the 26th. The model used the key TRUPPENVERSCHIEBUNG from a historical reference. Astra verified the cruiser’s arrival using original naval logs. The key was not known to have been used before December 9, 1918. The cipher was part of a list of 50 unsolved historical codes. This is the first known decryption of this specific message.