Generative engine optimization (GEO), defined: being retrieved, cited and represented by AI engines

What GEO means

A generative engine does three things with a brand before a buyer sees it: it retrieves pages that mention it, it decides whether to cite any of them, and it composes a description. GEO is the practice that works on all three. The retrieval third is technical (can the crawler reach you, is the page extractable). The citation third is editorial (is there a passage worth quoting). The representation third is reputational (what do the pages the engine trusts say about you). Practitioners sometimes call the whole thing "LLM SEO".

GEO is brand-level. It counts a mention on a reviewer's list as a win even when your own page is not the source. That is the main line between it and answer engine optimization (AEO), and AI visibility is the measurement both are trying to move.

GEO versus AEO: why the terms blur

No consensus definition exists. The pages that rank for either term each draw the line in a different place, some treat the two as synonyms, and every vendor defines them where its product sits. We say so plainly rather than pretend a standard exists. Here is where we draw the line, and why.

If you only have budget for one, do the one your measurement says is missing: if engines name you but never link you, that is AEO work; if they never name you at all, that is GEO work, and it starts off your site.

The engines

Each engine retrieves differently, and each has its own crawler token that decides whether it can read your pages. The full list by role is on the crawler tokens page; the engine-by-engine version is this.

• ChatGPT (OpenAI). ChatGPT search retrieves through OAI-SearchBot; a site that disallows it will not appear in ChatGPT search answers, per OpenAI's crawler page. Answers given without search draw on training data, which GPTBot governs, and OpenAI states that each setting is independent.
• Perplexity. Retrieves through PerplexityBot and answers with citations by default; Perplexity states that neither of its bots is used for training, per its crawler page.
• Gemini (Google). The Gemini app grounds answers with Google Search, and Google-Extended is the token that governs grounding in Gemini Apps and Vertex AI as well as training (Google's common crawlers page, last updated 14 July 2026).
• Claude (Anthropic). Claude-SearchBot and Claude-User are the retrieval agents; ClaudeBot is the training crawler, per Anthropic's help article.
• Google AI Overviews and AI Mode. Retrieve from the core Search index through Googlebot, use query fan-out, and add no requirements beyond being indexed and snippet-eligible (Google's guide to generative AI features). Since 31 August 2026 the Search Console "Search generative AI" control can exclude a site from both, with no public trace.

What the research says works

We only cite studies we can name, with a label. "Vendor" means the publisher sells in or near this category; "academic" means a peer-reviewed or preprint paper with its own benchmark.

• Quotations, statistics and cited sources on the page. The paper that coined the term (Aggarwal and colleagues, IIT Delhi and Princeton, arXiv 2311.09735, first submitted 16 November 2023 and revised June 2024) built a benchmark of 10,000 queries and reported that its best methods lifted a source's visibility in generated answers by up to 40% on the authors' own position-adjusted word-count metric, with quotation addition the strongest single method and keyword stuffing no better than doing nothing. The main evaluation used a gpt-3.5-turbo setup, with a confirmation run on Perplexity, so treat the size of the effect as a 2023 benchmark result, not a 2026 live-engine guarantee (academic).
• Third-party lists carry the citations. Wix Studio's AI Search Lab analysed 75,000 AI answers and over 1 million citations across ChatGPT, Google AI Mode and Perplexity: listicles 21.9% of citations, articles 16.7%, product pages 13.7%; listicles took 40.9% of citations on commercial queries and articles 45.5% on informational ones (vendor, reported by Search Engine Land, 24 March 2026).
• Rank inside those lists matters. Peec AI's analysis of about 200,000 AI responses across eight engines (September 2025 to March 2026) found that rank one in a cited listicle lifted B2B SaaS brand mentions by 16.5 percentage points and emerging MarTech mentions by 13.4 (vendor).
• On your own domain, depth beats lists. SE Ranking's fabricated-brand experiment (825 prompts, 15,835 AI answers, five AI systems, first month of a 16-month study) found deep guides drew about 900 AI answers per page, review articles about 257, comparison pages about 145, how-to pages 22, "best of" lists 11 and "alternatives" lists 4 (vendor, reported by Search Engine Land, 29 April 2026).

Read together: put quotable specifics on your own deep pages, and spend the rest of the effort earning rows, high rows, in the third-party lists engines already cite. What none of these studies show is a shortcut file or a special schema that moves an engine; Google's guide says it ignores those, and the other vendors publish nothing that says otherwise.

What to measure

1. Mention rate per engine on a fixed prompt set, with the number of runs and the sample size on every point.
2. Position when mentioned: first name in the shortlist or last.
3. Citation share: which domains feed the answers in your category, and whether yours is among them. That list is your outreach list.
4. The description itself. Read the verbatim answer for accuracy: a wrong price or a retired product name in an answer is a GEO defect no dashboard tile shows.
5. Google's impressions in AI Overviews and AI Mode from the Search Console Generative AI report (exposure only; it shows no clicks and no queries).

Hold any report, ours included, against the IAB's 3 August 2026 guideline: fewer than 50 queries per programme is exploratory; multiple responses per query; at least two intent types; results per platform. Whatever tool you use, make it show its sample. ClarAI's fix list ranks the pages to change and the mentions to earn, and the next scheduled run measures the move; we explain how the retrieval side is modelled in reading query fan-out like a map. The free grader covers readiness only, not visibility.

GEO in the UK

In the UK the term keeps its British spelling in searches ("generative engine optimisation") and in agency copy, while the pages that rank for the definition carry US-spelled titles; that is why the heading on this page is spelled the way it is and the body is not. The UK scene is agency-led: the "best GEO agencies UK" lists name agencies and no tools (Passion Digital's list of eight, 11 May 2026, is typical), and the trade press wraps the whole discipline as "AI search". brightonSEO's autumn edition runs on 8 to 9 October 2026, and the spring write-ups already carried "Generative Engine Optimisation" and "Answer Engine Optimisation" as standing session themes (Priority Pixels, 7 May 2026).

For a UK agency the practical points are short. The crawler tokens are global. Google's Generative AI report and its Search generative AI control apply to UK properties like any other since 31 August 2026. And the tools quote in US dollars, ClarAI included, so say so on the proposal rather than let the client find out on the invoice. What ClarAI ships for agencies today, and what it does not, is on the agency page.

Glossary: ten terms, one line each

Generative engine

An AI system that retrieves sources and composes an answer: ChatGPT, Perplexity, Gemini, Claude, Google AI Overviews and AI Mode.

Retrieval

The engine fetching pages to build an answer; governed by the retrieval crawler tokens, not the training ones.

Grounding

Anchoring an answer in fetched sources; Google-Extended governs grounding in Gemini Apps and Vertex AI.

Representation

How the engine describes you: accurate or not, positive or not, current or stale.

Query fan-out

Google's term for splitting one question into sub-queries searched separately before the answer is composed.

Third-party presence

Mentions of your brand on domains you do not own; the page type engines cite most.

Citation share

The domains an answer links to, and whether yours is among them.

Mention rate

The share of sampled answers that name the brand; the base of most scores.

Google-Extended

Google's robots token for Gemini training and grounding; it does not affect AI Overviews or AI Mode.

Monitored engine

In ClarAI, the four engines read on every plan: ChatGPT, Gemini, Claude and Google AI Overviews. Perplexity and Google AI Mode are not monitored.