Look up stuff where? Some things are verifiable more or less directly: the Moon is not 80% made of cheese,adding glue to pizza is not healthy, the average human hand does not have seven fingers. A “reasoning” model might do better with those than current LLMs.

But for a lot of our knowledge, verifying means “I say X because here are two reputable sources that say X”. For that, having AI-generated text creeping up everywhere (including peer-reviewed scientific papers, that tend to be considered reputable) is blurring the line between truth and “hallucination” for both LLMs and humans