WashU research finds gaps in Google AI Overview citations, claims

Since its launch in 1998, Google, the world’s leading search engine, has transformed how people find information online. For years, search results appeared as ranked lists of sources: Google decided what to show, but users decided what to read and whom to trust.

However, the advent of Google AI Overviews has fundamentally changed that paradigm. Today, when a user searches anything from “How long do I boil eggs?” to “How do I lower my cholesterol?” there’s a good chance the response will lead with a single artificial intelligence (AI)-generated summary. This change gives Google unprecedented editorial control over what users read and know, according to Jacob Montgomery, a professor of political science in Arts & Sciences at Washington University in St. Louis.  

“Google is now writing answers, not just ranking them, and it does this for billions of searches,” Montgomery said. “Yet we know very little about how the system works. When does an overview appear? Which sources does it draw on? Are the summaries accurate? And what happens to the rest of the web when people no longer click through? Our goal was to answer these basic questions.”

A forthcoming paper, to be presented at the October 2026 ACM Internet Measurement Conference, offers the broadest independent audit of Google AI Overviews to date — examining AI Overview activation patterns, source selection, whether claims matched their sources and the potential impact on publishers’ advertising revenue. The co-authors are Umar Iqbal, an assistant professor of engineering at WashU McKelvey Engineering, and Haofei Xu, a graduate student in the WashU Division of Computational and Data Sciences.

Conversational searches most likely to trigger AI Overview

Altogether, the researchers ran 55,393 Google searches on trending topics over 40 days, from March 13 through April 21, 2026. They collected each AI Overview, its citations, the first-page search results displayed with it and the content of cited webpages.

The research showed AI Overviews appeared for 13.7% of all queries, but the rate varied sharply based on how users worded their search. Nearly 65% of question-form queries produced an overview, compared with 9.5% of other searches. Longer searches also were more likely to trigger AI-generated answers. Among non-question searches, the activation rate rose from 9.9% for one-word queries to 38.7% for queries of six words or more.

This pattern suggests people seeking explanations in natural language rather than key word searches are more likely to encounter AI-generated material, Montgomery explained. Topic also mattered. Overviews appeared for 46.1% of hobby and leisure searches and 39.9% of science queries, but for only 7.5% of political searches and 9.6% of law and government queries, suggesting Google’s triggering logic relies on undisclosed editorial discretion.

Credible sources don’t guarantee claims

Across 61,212 citations, the domains cited by AI Overviews received higher average credibility scores than the traditional first-page results shown for the same searches. The overviews also relied less heavily on user-generated content.

Still, 29.8% of the cited domains did not appear in the first-page results. The researchers said the difference indicates that Google uses a source-selection process for its AI summaries distinct from its conventional search-ranking system. An average overview cited about eight sources.

Credible sources, however, did not guarantee that the generated summary represented them accurately. The team separated the overviews into 98,020 verifiable claims and checked each one against the cited webpages. About 89% were clearly or broadly supported by the sources. The remaining 11% included claims not found in the cited text the team was able to collect (7%) or claims that contradicted the cited source (4%).

‘Readers still need to check what they’re told, even when the citations look trustworthy.’

— Jacob Montgomery

The authors cautioned that the 11% error rate should be treated as an upper limit. Their pipeline could not fully capture content posted by ordinary users, such as Reddit threads, forum posts and YouTube videos. Rapidly changing information, such as weather forecasts and school closings, also may have been updated between the Google overview and when researchers captured the page.

Only 41.9% of the overviews were fully grounded, meaning every verifiable claim was supported by the available cited text. Because some cited pages could not be fully collected, this figure is likely conservative.

“Google’s summaries generally draw on credible websites, which is good news. But quality sources are not enough,” Montgomery said. “In a meaningful share of cases, we could not find support for a claim in the pages Google cited. Readers still need to check what they’re told, even when the citations look trustworthy.”

AI Overviews could affect advertisers, publishers

Finally, the study also examined the financial stakes for publishers. When an overview answers a question directly, publishers may lose the visit that generates advertising, subscription or sales revenue. In this study, more than half of the cited webpages displayed advertising.

The researchers didn’t directly measure traffic or revenue losses. However, they found that 2.2% of search pages containing an AI Overview also displayed a Google-sponsored ad, including 39 pages where an ad appeared above the overview. That arrangement, they wrote, may preserve Google’s ad revenue while giving users less reason to visit the publishers whose content informed the answer.

“Google’s AI Overviews are built on content that publishers pay to produce, and many of those sites depend on advertising revenue,” Montgomery said. “If people get their answer from the overview and never click through, those publishers lose the visit and the revenue. We did not measure that loss directly, but the incentives are worrying. Over time, Google and publishers will need to work out licensing or revenue-sharing arrangements, or the sites that AI Overviews rely on may not survive.”