The citations at the end of a research paper should represent a solid foundation of existing knowledge about a particular field, a pool of peer-reviewed sources built over years of research and study. However, with the increasing use of AI and large language models in writing research papers, there’s a growing chance that the citation someone clicks on may not even exist, and that the study, the source, or even the researchers themselves could be entirely fake.

In a recent study posted to the arXiv preprint server, researchers audited millions of papers and found that an estimated 146,900 hallucinated citations were present in research papers hosted on four major scientific repositories— arXiv, bioRxiv, SSRN, and PubMed Central. These numbers were for 2025 alone.

The hallucinated citations were not limited to a handful of bad apples but appeared across many papers, each containing a small number of fake references, pointing to a broader pattern of researchers using AI yet failing to fact-check the output.