I agree that GPT4 is better, but the amount of times it still hallucinates is still way too high to be useful for any real work. LLMs at present are super impressive, but have very very low trust.(This is true for all models, Claude, Opus, etc.)
Firstly, there is absolutely no way anyone could know this. Secondly, no they aren't.
Just as one can say, in response to a perfectly correct answer, "Explain what's wrong with your answer" and it will find something, one can either create a vacuum it feels compelled to fill with hallucinations or ask in a way it stays grounded.