ChatGPT-6 Astra cracks 217-year-old Napoleonic code in just six hours

What happened

What makes this impressive isn't actually the codebreaking, but that Astra completed the entire multi-modal workflow in ~6 hours from a single image and goal.1/6🧵 https://t.co/vyiGKOsrHq September 30, 2026 The message that was deciphered wasn’t directly from Napoleon. An AI engineer used GPT-6 (large language model by OpenAI) Astra to reveal the contents of a cipher that hadn’t been read since the Napoleonic Wars. OpenAI is an artificial intelligence company based in San Francisco, and its products and services include ChatGPT.

The task was initiated with a single image and prompt, and took just six hours from start to finish. Carter Church, an engineer at cybersecurity company SentinelOne, used Astra to crack the message hidden in 217-year-old code which had sat unsolved among Cryptiana's Unsolved Historical Ciphers list for decades.

OpenAI’s LLM (the kind of AI system trained on text to produce text) unpicked it within six hours, says Church, and it did so after only being fed a single image and prompt. You can download the “full solution package, with a script that regenerates the reading,” directly from Carter Church’s blog (download link in the first paragraph).