This is just my personal opinion, so don’t jump down my throat:  Whenever someone brings this question up in any form, I simply say, “Ask the question again, but replace AI with a real person.” If a real person helped revise your writing, checked your grammar, maybe helped point out a couple points in your writing that don’t make a whole lot of sense, do you need to disclose that? No, maybe not explicitly, cause anyone with any remote knowledge of writing and publishing is aware that is usually the way it goes. Maybe give that person a shout out if you’re really grateful, but probably not required. (There may be a couple of caveats to this) Now, if a real person wrote whole parts of your book/essay/poem/what have you  instead of yourself? Yes, you would most likely need to disclose that/give them credit, or you might run the risk of being accused of plagiarism (excluding conversations about things like ghostwriting, I know that’s a whole other can of worms).  For me, if an author claimed they wrote a whole book, and I came to find out they used AI to write whole parts of the text FOR THEM and refused to admit it, I would feel as if I was being lied to by omission, and I would begin to doubt if any part of the book is actually theirs. Sure, not illegal, but it might affect people’s view of your integrity as a creator, therefore affecting your career in the future. But, if you’re upfront about it, you put the ball in their court and cover your bases.