Hallucination & Groundedness

Fluent, confident, and not in the source

A hallucination is a statement the model produces that is not supported by anything it was given. It is usually fluent, plausible and delivered with the same confidence as everything else.

It is not deception and not a bug. The model completes patterns, and a free-postage clause is exactly the kind of thing that usually follows a refund policy.

Groundedness is the narrower, more checkable version: is every claim in the answer traceable to the supplied sources? That can be measured per claim, which is why it makes a better metric than the general question of truth. Asking the model to be more careful is not a control; checking claims against sources is.