← Concept IndexDEFINITION WHY IT MATTERS COMMONLY CONFUSED WITH
Hallucinations and unsupported claims
Also called: fluent is not true, confabulation, making things up
A hallucination is fluent, confident output that isn't supported by fact or by the sources provided. It arises because the model optimises for plausible-sounding text, not for truth.
The failure looks exactly like success — well-formed sentences, invented citations, realistic names. Fluency is not evidence, so claims that carry risk must be verified against a real source.
Lying. There is no intent; the model has no concept of true or false, only of likely-next-text.