When the first commercial AI detectors arrived in late 2022 and early 2023, it wasn’t exactly an auspicious start. News articles and social media posts showing AI detectors flagging the Declaration of Independence and the opening lines of the Book of Genesis as AI-generated were soon making the rounds. Either the Founding Fathers were also using AI to cheat on their homework, the comments sections quipped, or AI detectors did not work as advertised.

These false positives — instances when detectors label human-written text as AI-generated — were due to how the initial models worked. They evaluated how surprising a given text’s word choice was (a measurement called perplexity ) alongside how often those surprising choices were dispersed throughout ( burstiness ).…