The Short Version
Hallucination rates above 20% are documented in specific high-stakes domains like medical literature review and clinical decision support, but the claim's unqualified framing suggests this is typical across all AI language model use — which the evidence does not support. Broad benchmarks show top current models averaging under 10%, and sometimes below 1%. The rate varies dramatically by model, task, domain, and how "hallucination" is measured, making a single blanket figure misleading.