How does Google pick the sources in AI Overviews and AI Mode?

Direct answer

Google documents that AI Overviews and AI Mode draw on the Google Search index: a page appears there if it is indexed and eligible to be shown with a snippet, with no additional requirements. AI Mode also opens several related searches in parallel and brings the results together into one response. In the Observatory, 2,050 of the 2,076 Google AI Mode answers from the September 2026 cut arrived with at least one cited domain, spread across 1,308 distinct domains.

What Google documents

Google documents that, to appear in AI Overviews and AI Mode, a page has to be indexed and eligible to be shown with a snippet in Google Search, and it states that there are no additional requirements or special optimizations¹. Read plainly, the requirement is the familiar one: enter the index and stay eligible for a snippet.

On AI Mode, Google describes a query fan-out technique: it issues several related searches concurrently across subtopics and across several data sources, and brings those results together into one response². The consequence for a brand is that the query deciding which sources enter rarely matches the one the person typed.

Google also publishes a guide on its generative features where what it dismisses informs as much as what it recommends: it states that appearing there calls for no extra machine-readable files, markup or markdown, and it dismisses content chunking, an AI-specific writing style and the pursuit of inauthentic mentions as special techniques³.

What the site controls and how to verify access

The site owner's control is robots.txt for Googlebot¹. That is the first check: a Googlebot block leaves the site out of the index and, with it, out of both features.

The second is about snippets, and it is the one found misconfigured most often. Google documents that the nosnippet directive prevents the text snippet in results and also prevents the content from being used as a direct input for AI Overviews and AI Mode, and that max-snippet limits how much may be used, with the exception of a publisher having separately granted permission⁴. A site that set max-snippet to a small value to protect its content is at the same time limiting its entry into the generative features.

The third check works per section of the page. The data-nosnippet attribute marks stretches so they are left out of the snippet, and structured data declared inside a data-nosnippet element remains usable⁴. An answer block marked that way stays out of the direct input, and the schema in that same area is still read.

What my data shows for Google AI Mode

The Observatory queries the real Google AI Mode product. In the September 2026 cut, 2,050 of its 2,076 answers arrived with at least one cited domain, across 1,308 distinct domains. Counting one appearance per domain per answer they add up to 6,514 appearances, about 3.2 for every answer that came with sources; the count of individual citations, which counts twice a domain cited twice inside one answer, comes to 6,582.

The head of that list has a shape of its own. The domain appearing in most Google AI Mode answers is instagram.com, with 5.4% of the model's appearances, followed by youtube.com with 4.7%, reddit.com with 4.7% and gub.uy with 4.5%. These are surfaces where a brand rarely runs the page.

The contrast with ChatGPT, in the same cut and over the same prompts, shows two different splits. ChatGPT rests 11.0% of its appearances on a single domain, gub.uy, the Uruguayan state's. Google AI Mode spreads wider, and its first domain holds 5.4%. A brand measuring its presence in sources through one engine is also measuring the shape of that engine.

Google's two surfaces resemble each other more than either resembles ChatGPT. Of the 1,308 domains Google AI Mode cited, 774 also appear in Gemini's citations, 59.2%, and 537 in ChatGPT's, 41.1%.

On the searcher's side, the Pew Research Center, a research centre with no SEO product, measured across 68,879 searches by 900 US adults in March 2025 that 18% of searches produced an AI summary, that 88% of those summaries cited three sources or more, and that a click on a source cited inside the summary happened on 1% of visits⁵. The citation is visible, and the visit it returns is small.

How I measure it

I run the category's unbranded prompt bank against the real AI Mode product, three times per question and per model, and store per answer the brands named and the domains cited. I measure AI Mode separately from Gemini, on its own series: they are two surfaces from the same provider, with two different retrievals.

Before the first run I review robots.txt for Googlebot and the site's snippet directives, and I repeat that review whenever either of them changes.

I normalise every cited domain to its registrable domain, I count one appearance per domain per answer, and I drop Google's own domains, which appear through the shape of the answer.

How to prepare your site for AI Overviews and AI Mode

1. Confirm that your pages are indexed and eligible to be shown with a snippet. Google documents that as the requirement, and adds that there are no special optimizations beyond it.

2. Search your templates for nosnippet and max-snippet before touching the content. It is the configuration mistake that turns up most often, and a short value set to protect the content leaves you out of both features.

3. If you marked stretches with data-nosnippet, review which ones. Google documents that structured data inside those stretches is still read, so you can protect a block of text and keep the schema.

4. Write with subtopics in mind as well as the main question. AI Mode issues several searches at once across different parts of the topic, so a page that covers one subtopic well has a door of its own.

5. Measure AI Mode separately from Gemini. They are two surfaces from the same provider with different retrievals, and blending them gives you an average that exists on no screen.

6. Set the traffic expectation below what the citations suggest. The Pew measurement puts a click on a cited source at 1% of visits, so that is worth saying before promising results.

Which AuraMetrics modules address this

Measure the brand with the category's prompts. Prompt Tracking runs prompts across the five engines: ChatGPT, Gemini, Google AI Mode, Perplexity and Claude.

See where AI cites the competition. AI Visibility Gaps identifies where AI cites the competition and leaves the brand out.

Cross ranking with AI presence. SEO vs GEO Gap shows the keywords where the brand wins in Google and AI leaves it out, and it runs on ChatGPT, Gemini and Google AI Mode.

Frequently asked questions

¿Se puede rastrear la visibilidad en ChatGPT, Gemini y Perplexity con una sola serie?

Each engine is tracked on its own series and its own window. Google holds two separate surfaces, AI Overviews inside the results and AI Mode as a conversation, and a measurement that blends them reports an average with no equivalent on screen.

¿Qué tiene que registrar una herramienta de rastreo de visibilidad en IA?

What a tool records next to every figure is the surface measured and the collection method. Two figures from the same engine collected in different ways look alike and describe different things.

How I measured it

Observatory of brands in AI: a fixed bank of unbranded prompts across 35 categories in Uruguay, three repetitions per model, querying the real ChatGPT, Gemini and Google AI Mode products. September 2026 cut, read on September 25, 2026: 2,076 Google AI Mode answers, 2,050 with at least one cited domain, 1,308 distinct domains, 6,514 appearances and 6,582 individual citations. ChatGPT, in the same cut, 2,076 answers, 6,476 appearances and 6,922 individual citations, with 11.0% of its appearances on gub.uy.

Declared scope: domains are normalised to the registrable domain, so a subdomain counts with its site, and the engines' own domains are excluded. The Observatory covers Uruguay, so the head of the list reflects that market. The Observatory holds three cuts and this guide's figures come from the last one; a sum of cuts takes in a partial one, so every figure travels with its declared cut.