I get how you'd detect AI generated images, video, and voice. Being able to watermark those things at a metadata level or encode a signature into it. But I don't see any way it could possible do that for plain text that is copy/pasted.

Realistically, it would have to be just like existing plagiarism checkers, and just do a match search on text that it has generated itself (rather than searching published works or online) but that only covers stuff that ChatGPT has generated, not other ones that are yet to be made public, or self hosted GPT3 generations.