Hallucination propagation refers to the phenomenon in large language models and generative artificial intelligence where an initial factual inaccuracy, ungrounded claim, or erroneous token cascades into subsequent generation steps, causing further hallucinations. Because autoregressive models and multi-step reasoning systems treat previously produced text as valid context, an early error is adopted as an established premise rather than recognized as a mistake. This dynamic leads to a compounding effect where false information is reinforced and amplified across consecutive sentences, extended reasoning chains, or interacting agents, making downstream outputs increasingly untruthful and significantly harder to detect and correct.