In the text, we did share one hallucination benchmark: Claim-level errors fell by 33% and responses with an error fell by 18%, on a set of error-prone ChatGPT prompts we collected (though of course the rate will vary a lot across different types of prompts).

Hallucinations are the #1 problem with language models and we are working hard to keep bringing the rate down.

(I work at OpenAI.)

Optics. It would be inconvenient for marketing, so they leave those stats to third parties to figure out.