By asking models to complete sentences from a book, Gemini 2.5 regurgitated 76.8 percent of Harry Potter and the Philosopher’s Stone with high levels of accuracy, while Grok 3 generated 70.3 percent.
Ugh. We're back to this nonsense? "Finishing sentences" != "Memorizing entire books"
Finish this sentence: "We could have been killed—or worse, _______"
Turns out that if you take every sentence from a popular book like Harry Potter and the Sorcerer"s Stone, remove a few words at the end, and then ask an LLM to finish it, it'll get it right most of the time.
This is true for LLMs that have not been trained with that book.
Why is this, then? How is it possible that an LLM could complete sentences so effectively? Even when it hasn't been trained on that specific novel?
Human works aren't as unique as you think they are.
The only reason why LLMs work in the first place is because human writing is so easy to predict that you can throw an RNG at any given prompt and plug that into a statistical model of the most likely word to come after any given word and get a result that sounds legit. That's why it hallucinates all the time! It's because it's just a word prediction machine.
An AI model is not a database. It doesn't store books. It doesn't even really memorize anything. It's literally just an array of arrays of floating point values that predict tokens.
It's also wickedly complicated and seems like magic. If you don't understand how it works it's easy to fall into the "it's plagiarism!" beleif. It's not. If you believe that, you have been fooled! You're believing that it's actually intelligent in some way and not just a statistical representation of human output.
There's all kinds of things bad about commercial LLMs but "memorization" isn't one of them. That's an illusion.