Posting for visibility a reminder that this type of watermarking is comically easy to beat. See Scott Aaronson's 2023 research in which he coined the term "pineapple attack": one must simply prompt the model to add the word "pineapple" after every other word and then do a search + replace to remove the word, to obliterate the watermark altogether.
https://www.youtube.com/live/2Kx9jbSMZqA?si=0QgCPBX2_KPZ0QTU...