Definition
Plain language
When an AI confidently states something that isn't true.
As stated in the literature
A failure mode in which a language model generates content that is fluent and confident but factually incorrect or unsupported.
Also called: hallucinations, hallucinate, hallucinated, hallucinating
Why it matters: It's the central reliability problem with language models — useful output and fabricated output look identical until you check, which limits where they can be trusted.
For example, a model might confidently cite a paper by 'Smith et al. 2021' that doesn't exist, complete with a plausible-looking title and journal.
Heard on the show
“If the LLM hallucinated something — invented an API that doesn't exist, claimed a struct field that isn't there — the compiler catches it.”Episode 014 — Why a Constrained Pipeline Beat a Full Coding Agent at Finding Bugs 30-to-1