GPT-6 Astra decodes 217-year-old cipher letter to Napoleon's marshal

Carter Church says GPT-6 Astra transcribed and decoded the March 1809 letter to Auguste de Marmont in about six hours of model execution, working from a single scanned image. The cipher held 1,300 units and 155 distinct signs; a partial key from historian Daniel Tant covered 33 letter values (~435 units), with the rest solved via simulated annealing.