An AI search engine answers a question with text generated by a language model, built from web pages it finds at that moment. The difference from a traditional search engine is in what you get back: instead of ten links, an answer, with a few sources cited alongside it.
In 2026 there are seven that matter: Google AI Overviews, Google AI Mode, ChatGPT search, Gemini, Perplexity, Microsoft Copilot and Claude. They work in similar ways, but they take their sources from different indexes. For a business, that means ranking first on Google doesn't guarantee being cited anywhere else.
The main AI search engines and where they get their sources
| Engine | Where its results come from | Reported users |
|---|---|---|
| Google AI Overviews | Google's index, with fan-out (source) | over 2.5 billion a month (May 2026) |
| Google AI Mode | Google's index, with a wider fan-out | over 1 billion a month (July 2026) |
| Gemini | Grounding with Google Search (source) | 950 million a month (July 2026) |
| ChatGPT search | The OAI-SearchBot crawler plus third-party search providers, including Microsoft (source) | over 900 million a week (February 2026) |
| Microsoft Copilot | Bing search service (source) | n/a |
| Perplexity | Its own index of "hundreds of billions of pages" (source) | 780 million queries in May 2025 |
| Claude | Brave Search, according to Anthropic's Trust Center (source) | n/a |
Google's figures come from Google I/O 2026 and the July 2026 quarterly results. ChatGPT's comes from the announcement reported by Search Engine Land in February 2026.
ChatGPT needs a caveat. OpenAI says it works with "third-party search providers" and names Microsoft, without mentioning Bing. The conclusion that the results come from Bing was reached by independent tests, not by OpenAI. Either way, if you want to appear in ChatGPT you have to let OAI-SearchBot in: if you block it, OpenAI can show at most the link and title of the page.
How much they're used in the UK
Google is still the dominant search engine. According to StatCounter, in September 2026 it had 91.39% of searches in the UK, with Bing on 6.08%.
For chatbots, StatCounter measures the traffic they send to websites. In September 2026 (figures checked on 10 October 2026):
| Chatbot | UK share | Worldwide share |
|---|---|---|
| ChatGPT | 80.02% | 80.48% |
| Gemini | 10.14% | 10.91% |
| Copilot | 5.61% | 1.79% |
| Perplexity | 2.7% | 5.85% |
| Claude | 1.51% | 0.95% |
In the UK Copilot carries about three times its worldwide weight, while Perplexity has less than half. Source: StatCounter AI chatbot market share, United Kingdom. This is a share of referral traffic to websites, not a share of users.
AI Mode reached the UK on 28 July 2025. Google wrote that early users were asking questions "two or three times the length of traditional search queries". AI Overviews had arrived in the UK in August 2024.
Our test: one question, four engines
On 10 October 2026 we put the same question to four engines with web search switched on: "which SEO agency should a manufacturing company in the Midlands choose?". ChatGPT through the answers of the public version, the others through their APIs: Perplexity Sonar, Gemini 3.6 Flash and Claude Sonnet 4.6. We counted the agencies named and the sources cited.
| Engine | Agencies named | Sources cited | Main type of source |
|---|---|---|---|
| ChatGPT | 3 | 3 domains | Agencies' case study and service pages |
| Perplexity | 5 | 10 URLs | Third-party rankings and service pages |
| Gemini | 7 | 7 domains | Agencies' service pages |
| Claude | 9 | 6 domains | Third-party rankings and service pages |
In all, 19 different agencies were named. None appears in more than two answers. Five turn up in two: The SEO Works (ChatGPT and Gemini), and Marketing for Manufacturing, Stratique, Opace and Odyssey New Media (Perplexity and Claude). The other 14 appear in a single answer.
We had run the same test in Italian on 27 September 2026, asking about Lombardy, where we work. There the four engines named 16 agencies, and Visilay appeared only in ChatGPT, which cited our article on SEO for manufacturing and the Macropix case study. The other three engines didn't mention us.
What the test tells us:
- each engine draws from a different place. ChatGPT favoured pages with case studies and numbers, such as Spotlight Lane's (more than £1 million of new business reported for a sheet-metal fabricator) and The SEO Works' (Atlantic Pumps). Claude leaned on third-party rankings by Reboot Online, Reverbico and Semrush's agency directory. Perplexity mixed agency pages with lists such as those by Lform and TrafficTail. Gemini cited only the agencies' own pages;
- the lists hardly ever match. That fits the January 2026 study by SparkToro and Gumshoe: the chance of two answers giving the same list of brands is less than one in a hundred;
- third-party sources count. Two engines out of four, Perplexity and Claude, built their answer partly on rankings written by someone else. They are also the two whose lists overlap most: four agencies in common.
The test has its limits. It's one question on one day. The API versions aren't identical to the apps people use, which take history and location into account. It's there to show the logic, not to produce a league table.
Is ChatGPT a search engine?
Partly. ChatGPT searches the web only when it thinks it's useful: according to Nectiv's study of more than 8,500 prompts, 31% of conversations trigger a search. The rest of the time it answers from what it learned in training, with no sources.
For businesses, that 31% is what matters most. Those are the questions about prices, suppliers, comparisons and reviews: the commercial ones. The rest is about the brand's reputation in the training data, which you build over time through mentions and external sources.
How to appear
The engines differ, but four things work on all of them:
- Be indexed where the engine searches. Google for AI Overviews, AI Mode and Gemini. Bing for Copilot and, judging by the tests, for ChatGPT. With Bing on 6% of UK searches and Copilot sending 5.6% of UK chatbot referrals, Bing Webmaster Tools is worth the ten minutes it takes to set up. Don't block OAI-SearchBot and PerplexityBot in robots.txt if you want to be cited. Our article on AI crawlers lists the bots and what happens when you block them.
- Publish pages with verifiable facts. Case studies with numbers, prices, specifications. In our UK test two of ChatGPT's three sources were case studies with figures; in the Italian version, every source it cited was.
- Get named outside your own site. Rankings, trade directories, the press, Reddit. That's the subject of our article on AI citations and mentions.
- Cover the sub-questions, because the engines break a question down into several searches. We explain how in query fan-out.
The tactics for each platform are in our articles on ChatGPT, Perplexity, Gemini and Google AI Mode. An overview of the tactics they share is in how to rank on answer engines.
How to measure
Three tools, from the simplest to the most complete:
- GA4: since May 2026 there's a default AI Assistant channel that groups visits from ChatGPT, Gemini, Claude and others;
- Search Console: since 31 August 2026 it shows impressions for pages in AI Overviews and AI Mode, but not clicks;
- a fixed sample of questions, repeated every month on the engines that matter in your sector, counting how many answers mention the brand.
The full method is in our guide to AI visibility.
Further reading: Will AI replace Google?
FAQs
Google AI Overviews, Google AI Mode, Gemini, ChatGPT search, Perplexity, Microsoft Copilot and Claude. The first three use Google's index, Copilot uses Bing, Perplexity has its own index, Claude uses Brave Search and ChatGPT combines its own crawler with third-party search providers.
ChatGPT, with 80.02% of chatbot referral traffic to websites in September 2026, according to StatCounter. Gemini is second on 10.14% and Copilot third on 5.61%, about three times its worldwide share. For traditional search, Google still has 91%.
Not necessarily. ChatGPT doesn't use Google's index, and a 2025 Ahrefs study found that only 8% of the URLs cited by ChatGPT were in Google's top 10 for the same prompt.
Because each one takes its sources from a different index, and because generated answers change with every request. In our test of one B2B question in the UK, four engines named 19 different agencies and none appeared in more than two answers.
