In breve
An AI hallucination is when an AI model produces information that sounds confident and plausible but is actually false, made up, or not supported by its sources. The model is not lying in any human sense; a language model works by predicting likely next words, so when it lacks the right facts it will often generate a fluent, confident answer anyway rather than say it does not know. Hallucinations range from a wrong date or a fake citation to an invented API method or a made-up legal case. Because the output reads as authoritative, hallucination is one of the biggest reasons you keep a human in the loop and verify anything an AI produces before you rely on it.
Why models hallucinate
Hallucination is a side effect of how language models work, not a random bug. A few causes show up again and again.
- Prediction, not lookup: the model generates likely text, so it fills gaps with plausible-sounding guesses.
- Missing or stale knowledge: if the fact was not in training and is not in the prompt, the model improvises.
- Pressure to answer: models are tuned to be helpful, so they tend to produce an answer rather than admit uncertainty.
How to reduce hallucination
You cannot fully remove hallucination, but you can make it much rarer. Ground the model in real data with RAG so it answers from retrieved sources instead of memory. Give it tools to look things up rather than guess. Ask for citations you can check, keep prompts focused so the right context is not buried, and lower the stakes by verifying output before acting. In agentic engineering, tests and human review are the safety net that catches a confident wrong answer.
Hallucination in agents
Agents raise the stakes because a hallucinated fact can become a hallucinated action: a coding agent might call an API that does not exist, or a research agent might cite a paper that was never written. This is why a good agent harness pairs the model with real tools (running code, searching, reading files) so claims get checked against reality, and why verification stays a human responsibility. The honest posture is to treat every confident answer as a draft until something grounded confirms it.