3 October 2026. A note on the viral GPT-6 Astra / Napoleon cipher post, checked against Carter Church’s write-up and the Cryptiana page.
A post is doing the rounds. GPT-6 Astra cracked a 217-year-old letter to one of Napoleon’s generals. Six hours of model work. 1,300 cipher units off a bad scan. A published partial key. A solver. Historical letters to date it. Cryptiana now lists it solved. AI unlocked a piece of history that had sat unread for two centuries.
Most of that is true. The sentence is still wrong.
The letter is real. Late March 1809, from Eugène de Beauharnais, Viceroy of Italy, to General Auguste de Marmont, then stuck in Dalmatia with Austrian ground between him and every other French army. On 16 March Napoleon told Eugène, from Paris, to send Marmont where every French and allied army stood, in cipher, carried by an intelligent officer. The first line of the surviving letter is clear French. Twenty-four rows after that are numbers, stray letters, and invented marks. The only copy in circulation was a plate in Lieutenant-Colonel Vilcoq’s 1969 article, digitised by Persée at about nineteen pixels a sign. Cryptiana had it filed as 1807, and unsolved. The last serious note was that there was nothing to work on, because the ciphertext had never been published as text.
Carter Church, who says he had never broken a cipher, put GPT-6 Astra on that plate. About six hours of model execution. Not six hours of one prompt. The model cut the plate into rows, read the signs, and decided which of 175 hand-drawn marks were the same sign twice. That part of the viral post is the right instinct. There was no transcription to start from. Getting usable text out of the scan was the gate. It was not the whole job.
It did not start from a blank key. Daniel Tant had already published 33 letter values for this cipher, hosted by ARCSI. Those 33 values cover 435 of the 1,300 units. A third of the letter was readable before any new search. Cryptiana’s own note says the same thing: Tant’s key reads about a third. The other 865 units were worked out of the letter: a simulated-annealing solver, scored on French letter statistics, with signs that refused to be letters tested as whole words. Twenty-nine of them are words. On Church’s own key, five signs are still unresolved, carried as a best guess. Solved means a working reading. It does not mean every mark is settled.
The date is the part worth keeping, and it is his reconstruction, checked against a public letter rather than against the model’s confidence. The plaintext he publishes lists the same seven forces, in the same order, with the same figures, as Napoleon’s letter to Eugène of 16 March 1809, number 14908 in the Correspondance. The clear first line refers to letters of the 8th, 14th and 20th of the current month. Austria crossed the Inn on 10 April. On that match, the letter is the last days of March 1809, not the 1807 the list had filed. That is not the model having a feeling about history.
Cryptiana does now mark the entry solved. The page, as of this evening, says Church notified Satoshi Tomokiyo on 20 September 2026, and that the date should be corrected to 1809. The heading still says 1807. Solved is not the same as corrected. Nor is this the first time this autumn a model has been pointed at Tomokiyo’s list. Daniel Bourdeau has been clearing entries for weeks. Church says this one had already been tried, and left, because the ciphertext was only a plate.
What the viral post leaves out is the only part that matters if you buy software.
The solution is not a chat. Church published a zip: the plate, the transcription, the key, the French, the English, and a script that runs the key against the transcription and regenerates the reading with the model out of the room. He also says he reran the solver with Marmont’s memoirs and the Napoleonic texts stripped out, and got the same reading. So this is not “the model remembered the war.” I have not re-run the script. The point is that a stranger can.
That is the same test as the ledger. In the record, or beside it. The model did real work. It transcribed a plate nobody had typed, and it searched the two-thirds Tant had not already given away. It did not sign the result. Tomokiyo did, by marking the entry after he was told. Church did, by putting a file next to the claim. Attestation did not move to Astra. It never does.
If someone tells you the model cracked it, ask for the file. No key, no transcription, no check a stranger can run without the model in the room: you have a screenshot. Screenshots do not close.
Mark Hendy is a PE-facing CFO and the founder of Tanous. Views his own.
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