An AI search percentage needs a denominator

Share of its cited sources ChatGPT Search replaces every week, against 56% for Google, across 82,619 prompts re-sampled weekly for 17 weeks (1,548,213 snapshots, six countries) in a SISTRIX study — with a stable core of a few domains present for 86% of prompts and everything outside it rotating at 89% per week.

Share of the time Google AI Overviews and Google AI Mode cite different domains for the same prompt, per SISTRIX — two surfaces from one company that agree on source selection less than a fifth of the time, so a citation-share number measured on one is not a reading of the other.

Share of news articles cited as sources that remained permanently in the citation set across 17 weeks of weekly re-sampling, per SISTRIX — for a publisher an AI citation behaves less like an asset that accrues than a placement that expires. By contrast, 43% of brand queries kept the brand's own domain present in all 17 weeks while its co-citations rotated at 70% per week.

Typical error in a brand's measured AI mention rate when one prompt is queried on 20 days, against ±9.5 points for 20 different prompts and ±4.2 for 100, per Sistrix's analysis of 10,826 daily measurement series across four AI models and eight countries — for a brand that truly appears in 25% of answers, one prompt could read anywhere from 0% to 59%. Sistrix also reports that 70% of brands appearing in a prompt's answers show up on fewer than one in five days, and that a weekly average of 20 prompts is accurate to ±1.8 points against ±4.8 for a single day.

YouTube's mention share in Google AI Overviews — the most-cited domain, ahead of Reddit (18.5%), Facebook (10.7%), Google itself (7.1%) and Instagram (5.8%).

Share of AI Mode passages reused 100 or more times that come from pages already ranking #1 organically, per a Pillarbase study of 15.7 million citations; the most-recycled passages average 117 words, answer in the first sentence about 80% of the time, and are self-contained about 85% of the time.

Perplexity's rate of "ghost citations" — pulling from content without naming the source brand — the highest of seven engines Writesonic measured, followed by Google AI Mode (49%), AI Overviews (41%), ChatGPT (37%), Gemini (25%), Grok (22%) and Microsoft Copilot (19%), across roughly 16 million brand appearances.

Share of AI-cited pages that looked fresh by last-modified date versus by original publish date, among 4,124 pages with both dates in a Seer Interactive analysis of 47,097 citations across ChatGPT, Gemini and Perplexity — refreshed old pages outcited newly published ones. Overall, 75% of cited pages had been updated within the past year, 88% within two years; recency requirements varied by engine (Gemini 78%, ChatGPT 73%, Perplexity 65%).

Growth in Reddit's tracked search footprint between June 2025 and February 2026, with its AI citations up another 84% from February to July 2026 before plateauing at a level several times higher than a year earlier — Google AI Overviews drives roughly 88% of Reddit's citation volume, per a BrightEdge analysis using its AI Hyper Cube, Data Cube X and Expert Services datasets.

Relative drop in Reddit's share of ChatGPT Search citations — an average 3.83% (July 18-Aug 7) down to 0.52% (Aug 14-17) — against just an 11.3% decline on Google AI Overviews (2.37% to 2.10%) and 30.5% on AI Mode over the same window, per Promptwatch. It attributes the ChatGPT-only break to an August 8 change that pushed use of the site: operator in ChatGPT's background search queries from 0.37% to 16.8%, and calls the decline provisional pending confirmation it isn't a data-collection issue.

Reddit's share of ChatGPT citations, which fell from about 1 in 5 answers in March 2026 to 1 in 43 by late September — an 88% drop — while Wikipedia fell from 1 in 7 to 1 in 35, down 80%, per Ahrefs' Brand Radar data tracking 2.4 to 3.8 million ChatGPT answers a month. Over the same stretch the combined citation share of OpenAI's 17 licensed content partners more than doubled, from 7.5% in March to a July peak of 15.8%, easing to 12.5% by late September. Reddit still ranks ninth among domains ChatGPT searches directly with the site: operator, which Ahrefs reads as the model still fetching Reddit for opinions while citing it less.

Share of U.S. Google searches that sent a click to the open web in June 2026 (40.7% in the EU/UK) — a record low — while Google AI Mode held at just 0.13% of U.S. search-related visits, per Datos and SparkToro's Q2 State of Search report.

Year-over-year decline in People Inc.'s Google search traffic — now 21% of its total traffic, down from 25% the prior quarter, with core sessions off 22% YoY — even as the publisher's CEO says it won't block Google's AI crawlers because that "would turn off search."

Drop in Google AI Overviews' position-1 click-through rate in 2026, up from a 34.5% drop in 2025, per an Ahrefs analysis spanning roughly 15 million data points.

Average share of Google AI Overview citation-click traffic misattributed to the Direct channel instead of Organic Search in GA4, per a nine-month tracking study of 51,200 clicks across 1,661 AI Overview-cited snippets — worst in May 2026 at 29.3%. The same tracking found AI Overviews drove 7.53% of organic sessions overall, peaking at 16-17% in February-March 2026 before falling to 2-4% by August.

CTR lost by French sites most exposed to AI Overviews (over 20% of their queries triggering one), comparing the 28 days before to the 9 days after AI Overviews launched in France on July 22, 2026; the median site across 963 tracked domains lost 5.7% of CTR and 8.8% of clicks, and nearly 48% of sites lost more than 10% of daily clicks within nine days. Health queries lost the most — a 22.2% AI Overview trigger rate and a 20.4% CTR decline. Ahrefs' Juliette Begue, using Google Search Console data, found roughly "one point of CTR lost per point of exposure."

Reduction in outbound clicks per search when Google shows an AI Overview — from 0.62 down to 0.37 — in the first randomized field experiment on the question: 1,065 U.S. desktop searchers randomly assigned to see results with or without AI Overviews over two weeks in early 2026. Self-reported search satisfaction held flat at 4.0 out of 5 either way, and just 7.1% of outbound clicks on AI Overview-bearing pages came from links inside the AI-generated answer itself, with the rest going to ordinary organic results on the same page.

Citation-odds multiplier for a page carrying the current year in its title, versus a matched, uncited page on the same domain — the strongest of 43 page-level features tested, per Sistrix's conditional logistic regression across 48,527 pages cited by ChatGPT, Google AI Mode and AI Overviews in Q2 2026, matched against uncited same-domain pages (96,418 URLs, 17,380 domains). Other factors: a table of contents, used by only 14% of pages, carried a 1.7x factor; Article schema markup 1.6x; five or more H2 headings 1.6x; FAQPage schema 1.5x. Pages carrying many of these features were cited 2.1 times as often as minimally optimized ones; on ChatGPT specifically, a question-phrased title carried a separate 1.9x factor. The dataset covers the German-speaking (DACH) market.

Share of Google's People Also Ask boxes answered by an AI Overview in the first week of September 2026, per AlsoAsked's analysis of 19.2 million English-language queries — up from 86% in August, the last major SERP feature AI Overviews hadn't fully absorbed.

Share of roughly 100 large brand names that triggered a Google AI Overview when searched directly — including Reddit, Salesforce, Amazon, Adobe, Wikipedia, Samsung, Apple and Yahoo — well above the 43% aggregate rate across all Google searches, per researcher Chris Long. Most placements sat mid-page or lower rather than at the top; Google showed none for searches on its own name or on news publishers' names. Long found AI Overviews far less common on the same kind of brand search when he ran a similar test roughly two years earlier.