AI search engines choose sources by searching first and then linking the pages they used, and each one searches differently. Google works from its own Search index, ChatGPT sends rewritten queries to search providers, and Perplexity describes a search index of its own. None of them publishes a ranking formula or promises placement.
By Donnie Strompf. Updated October 2026.
Key takeaways
- Google says AI Overviews and AI Mode need nothing beyond a page that is indexed and eligible to show with a snippet.
- Each vendor documents a search crawler of its own, so allowing Googlebot does not cover ChatGPT, Perplexity or Claude.
- Perplexity’s engineering article describes its index and ranking pipeline but says nothing about how a business earns a citation.
- No vendor page names the factors that decide which sources appear, OpenAI says placement is not guaranteed, and Google says indexing and serving are not guaranteed.
How does each AI search engine pick and show its sources?
I’m Donnie Strompf, and I’ve done SEO since 2008. The table uses only what each vendor publishes about its own product. The last column names the pages I read on October 15, 2026, with the date each shows.
| Engine | How it finds pages | How sources are shown | What a site owner controls | Vendor pages read |
|---|---|---|---|---|
| Google AI Overviews | Google says an overview appears when its systems judge it additive to classic Search. It may run a “query fan-out”: related searches across subtopics and data sources. | A snapshot with links to web pages that support it. | The page must be indexed and eligible to show with a snippet. Googlebot robots.txt rules, nosnippet, data-nosnippet, max-snippet and noindex limit what is shown. | Google Search Central, “AI features and your website” (last updated December 10, 2025); Google Search Help page on AI Overviews (no date shown) |
| Google AI Mode | Google describes dividing the question into subtopics and searching each across multiple data sources at the same time. It says responses are supported by high quality web content. | A response with links to explore further, plus follow-up questions. Google says AI Mode gives a set of web links when confidence in a response is not high enough. | The same Search controls. Google says the two features may use different models and techniques, so links can differ. | Google Search Help page on AI Mode (no date shown); the Search Central page above |
| ChatGPT search | OpenAI says it typically rewrites a question into one or more targeted queries and sends them to search providers. It ranks results on multiple factors and does not list them. | Inline citations, and a Sources button that opens the cited links. | Allow OAI-SearchBot in robots.txt and allow OpenAI’s published IP addresses at your host or CDN. Placement is not guaranteed. | OpenAI Help Center, “ChatGPT search” (shows “Updated: last month”, no date); OpenAI bot documentation (no date shown) |
| Perplexity | Perplexity says it searches the internet and compiles what it finds into an answer. Its engineering article describes an index of over 200 billion URLs and a ranking pipeline that scores both whole documents and spans within them. | Numbered citations that link to the original sources. | PerplexityBot is designed to surface and link websites in Perplexity search results. Perplexity recommends allowing it in robots.txt and permitting its published IP ranges. | Perplexity Help Center, “How does Perplexity work?” (no date shown); Perplexity bots documentation (no date shown); Perplexity, “Architecting and Evaluating an AI-First Search API” (September 25, 2025) |
| Gemini app | Google says some Gemini responses are grounded on Search results. Google-Extended is the token that governs whether crawled content may be used for training Gemini models and for grounding in Gemini Apps. | Sometimes shows sources and related content within and below a response. Google says not all responses include links, and a large quote from a webpage adds a link in the sources list. | Google-Extended in robots.txt. Google says it does not affect a site’s inclusion or ranking in Google Search. | Gemini Apps Help page on related sources (no date shown); Gemini Apps Privacy Hub (last updated October 13, 2026); Google crawler documentation (no date shown) |
| Claude | Anthropic says Claude searches when a topic needs current information, or when the user asks it to. Claude-SearchBot navigates the web to improve search result quality. | Anthropic says responses include citations and source links. | Anthropic says blocking Claude-SearchBot may reduce your site’s visibility and accuracy in user search results. | Anthropic, “Does Anthropic crawl data from the web” (April 7, 2026); Claude Help Center, web search (no date shown) |
Google’s two AI features run on Google Search, so Google’s Search requirements apply to them. ChatGPT uses search providers and Perplexity describes its own index, and both publish crawler documentation.
What do the vendors not say about choosing sources?
OpenAI says ChatGPT ranks results “using multiple factors” and lists none. Google says AI Overviews appear when they are additive to classic Search and does not define the term. Perplexity’s help page says it gathers information from authoritative sources and does not say how authority is judged.
Perplexity’s engineering article is the most detailed description of any vendor here, and it explains how an index is built, not how a business earns a citation. A figure caption in it describes Perplexity itself as powered by the same search infrastructure that the article presents as a Search API.
Claims beyond the vendor documentation need independent testing, so check when a test ran and which prompts it used. Results also change: eMarketer reported on April 2, 2026, citing Search Engine Land, that 40% to 60% of cited sources change month to month across Google AI Mode and ChatGPT.
Which crawlers decide whether an engine can use your site?
Each engine reads pages through its own search crawler: Googlebot for Google AI Overviews and AI Mode, OAI-SearchBot for ChatGPT search, PerplexityBot for Perplexity and Claude-SearchBot for Claude. Gemini is the exception, because Google says its Google-Extended token governs training and grounding, and that it does not affect Search inclusion.
The full robots.txt table, with training bots, user-requested fetchers and llms.txt, is on our page about AI crawlers, robots.txt and llms.txt.
How do AI engines choose local businesses?
None of the vendor pages above describe a method for picking local businesses. OpenAI says only that ChatGPT may use an approximate location based on your IP address to provide relevant local results. Google’s local ranking page says local results in Search are mainly based on relevance and distance plus how well known a business is, and that there is no way to pay for a better local ranking (no date shown). It does not say those factors apply inside AI answers, so treat them as the nearest documented guide.
Third-party data on which local sources the engines cite, and the steps a local business can take, are in our guide on how to get recommended by ChatGPT and Google AI Overviews.
How can you tell which engine sent a visitor?
OpenAI’s publishers and developers FAQ (no date shown) says ChatGPT adds the parameter utm_source=chatgpt.com to referral URLs, so Google Analytics can separate those visits. Google says sites that appear in AI features are counted in the Web search type of the Search Console performance report, mixed in with regular search traffic.
When someone asks ChatGPT who to call, the business it names is the one that gets searched next. We do AI visibility alongside SEO, never instead of it.
What should you ask your agency or developer?
Use the differences above to ask your agency or developer these questions.
- Which search crawlers named above does our robots.txt allow, and does our host or CDN block any of them?
- Which engine did each reported citation come from, and which page of ours did it link?
- If a report says “AI visibility”, which prompts were tested, on what date, and in which engines?
Our AEO services page describes the work, and the SEO pillar guide covers the search basics that Google’s AI features rest on. AEO costs $950 to $2,000 a month alongside SEO, and every service price is on the pricing page. Our guide to how much AEO costs sets out the ranges.
FAQ
How do I check that my snippet settings work for Google’s AI features?
Google says to use the URL Inspection tool to check that preview controls are working. Run that check on a page after any change to a nosnippet or max-snippet setting, and again if the page stops appearing with the text you expected. Ask your developer to send you the result for each important page.
How do I check a ChatGPT answer about my business?
OpenAI warns that ChatGPT search results can be incomplete, outdated or incorrect, and advises checking sources and publication dates. A person can start a search by hand from the tools menu or with a slash, which makes repeat tests easier. Open each linked page and note the date it shows.
What is the difference between a Perplexity answer and Deep Research?
Perplexity’s help page says each answer carries numbered citations linking to its sources. It describes Deep Research as running dozens of searches automatically and reading hundreds of sources, with reports delivered in about 2 to 4 minutes. Ask which mode produced any citation report you are shown.
Can web search be switched off in Claude?
Anthropic says that on Team or Enterprise plans an owner must first enable web search under Admin settings, after which members can toggle it in a chat. Free accounts have daily usage limits that include web search. Check that web search is switched on before you test your business in Claude.
Does my Google Business Profile affect what Gemini says about my business?
Google documents no Gemini-specific profile control in the pages I read. Its Business Profile help page says complete, accurate details help Google match a business to relevant searches, and it recommends verifying the business, keeping address and business hours current, and responding to reviews. Those steps cost little, though Google does not promise an effect on Gemini.
Related reading
- Does AI Make Mistakes in Digital Marketing? A Channel-by-Channel Reality Check
- Can you pay to be recommended by ChatGPT or Google AI answers?
- What AI recommends for local services in Palm Beach County: a 120-answer study
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