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never used Claude, only Gpt , Gemini and grok and Gemini seems to be the most grounded out the 3 ,also it's about understanding how the tools work and building a workflow around it , i think it's possible to make full books with AI if you have the right workflow

I feel like they'll be easy to spot, with obvious tells. I suppose it doesn't matter once the book is "sold" though - as that's where the "profit" is made - but is it still a "good" story?

I guess but with time they can become better and people will not be able to tell

Some people can't tell. And like @bitcoinman says, they'll get better with time.

Each LLM has its strengths and weaknesses.