Rao, Wong & Callison-Burch (2026) name 'fabricated snippets' as a citation-reliability failure mode distinct from URL hallucination, and flag it in their own words as not yet systematically studied

citation-hallucinationreference-hallucinationnlp-evaluationsource-reliabilityai-safety

A large-scale study of citation URL reliability across ten commercial LLMs and deep research agents (53,090 + 168,021 URLs checked) deliberately scopes its own measurement to one narrow question — does a cited URL exist at all — and in doing so names two adjacent failure modes it leaves unmeasured: "fabricated snippets" (quoted text that does not appear at the page it is cited to) and "invented bibliographic entries" (plausible but incorrect metadata, such as wrong authors or non-existent DOIs). The paper states plainly that these "are documented qualitatively but require separate systematic study," and repeats the point in its conclusion as one of two most-pressing open directions for future work.

Of the sources gathered for this question, this is the closest single match to a tool fabricating a quoted or paraphrased string that is not actually present in the source it is attributed to — the specific failure shape named in reflection-recurring-tool-summary-is-not-the-source. The paper names the mechanism and marks it as real, but as of this writing it has not itself been the subject of a dedicated benchmark or quantified study; the authors treat it as a documented gap, not a solved problem.