GPT-6 Astra Breaks a 1941 Enigma Message Unsolved Since 2005

OpenAI's GPT-6 Astra broke a German Army Enigma message from July 10, 1941, that had resisted solution since 2005, according to Frode Weierud, the cryptanalyst whose research site lists it among the collection's unbroken traffic.

Carter Leffen, a product development coach at Bloomberg LP in New York, directed the model to attempt the message and reported the result to Weierud on Sept. 15, according to Weierud's account on the CryptoCellar Research site and a Sept. 17 report by The Decoder.

The GPT-6 Astra Enigma message, decoded after 85 years

The message, numbered 172 and carrying the indicator MVUEH, went out from a radio station with the tactical callsign 2ny to the radio station of the SS-Totenkopf Quartiermeister, Ib, according to Weierud's site. The Decoder reported the plaintext is a soldier's request for marching orders from the town of Rosenow, signed by a sender tentatively read as Waschbusch, with garbled words including "BTTE" for "BITTE" and the phrase "Sofort Funkantwort," German for immediate radio reply.

How Leffen narrowed 82 letters of ciphertext

Leffen ran a variant called GPT-6 Astra Extra High for about ten hours, according to The Decoder and a Sept. 21 post on the blog Schneier on Security. The model reused the place name Rosenow from a different message, Nr. 173, that had already been solved the same day, cutting the number of rotor settings it had to test before checking each candidate against Enigma's rule that a letter is never enciphered as itself.

MVUEH is German Army traffic from CryptoCellar Research's own collection, assembled from original message forms the site says it received starting in 2001, separate from the wartime Bletchley Park archive.

Date	Event
1941-07-10	Message MVUEH transmitted by radio station 2ny
2005	Message still listed as unbroken on CryptoCellar Research
2026-09-15	Leffen reports the completed break to Weierud
2026-09-17	The Decoder publishes an account of the break

The verification problem Weierud flagged

Weierud confirmed the break is correct, writing on his site that "the AI break of the Enigma message MVUEH is simply amazing, and as an old cryptanalyst, I am still in awe." He also raised a question he has not resolved. GPT-6 Astra cited two specific German military archive file references, RS 3-3/20a and RS 3-3/63b, that Weierud said are correct but are not published anywhere on his own website.

"It is not clear what this is, whether it has succeeded in accessing the Bundesarchiv's digitised collections or whether it has found these files elsewhere," Weierud wrote of the model's sourcing.

What is still unconfirmed

OpenAI has not commented publicly on the break. Neither Weierud's site nor The Decoder's report states which of GPT-6 Astra's working logs Leffen has released for outside review, and Weierud's own account says he has not been able to trace the two archive citations himself. The message is one of the last unbroken items in a collection of German Army Enigma traffic that CryptoCellar Research says it began working on in earnest in 2003, after receiving the original message forms in 2001; nearly all of the site's 1941 messages have now been solved.

The same week, GPT-6 Astra was also credited with a separate, disputed claim about a World War One-era cipher, and a robot-arm safety benchmark found the model completed 60 of 100 instructions a reviewer flagged as dangerous. Weierud's site does not say whether any further messages from the same 1941 traffic remain open for GPT-6 Astra, or any other model, to attempt next.