Key takeaways
An AI search engine answers a question with a written text, instead of a list of links. It combines what its model has learned with a web search run on the fly, then cites some of its sources. Each engine draws on its own index: Google, Bing, OpenAI, Perplexity or Anthropic.
- At the end of May 2026, ChatGPT held 46.4% of the AI assistant market, ahead of Gemini (27.7%) and Claude (10.3%), according to Sensor Tower.
- ChatGPT cites about 15 sources per answer, Gemini about 3 (Semrush, June 2026).
- For a website, blocking an engine’s index crawler means giving up on being cited there as a source.
What is an AI search engine?
An AI search engine, or answer engine, interprets a question in everyday language, looks for information and writes a summary answer. This answer often comes with links to its sources. A classic search engine returns a list of ranked pages; the AI engine does the reading and the summarizing itself.
| Classic search engine | AI search engine | |
|---|---|---|
| What it returns | A list of ranked links | A written text, with or without links |
| Form of the query | A few keywords | A full question, then follow-ups |
| Who does the summarizing | The user, by opening the pages | The language model |
| Place of the sources | Each result is a source | A few sources cited, sometimes none |
The boundary is blurring: Google builds AI answers into its results, and conversational assistants run web searches. For a website publisher, the useful question is therefore less “which tool” than “where do the cited sources come from”. That is the angle of this page, which complements our GEO guide.
What are the main AI search engines?
Six families of services matter in France in September 2026. They differ in their index, the way they cite and what they show publishers.
| Engine | Type | Search index used | Possible measurement for a site |
|---|---|---|---|
| Google AI Overviews | AI summary at the top of the results | Google index (Googlebot) | AI impressions in Search Console |
| Google AI Mode | Google’s conversational tab | Google index (Googlebot) | Same, aggregated with AI Overviews |
| ChatGPT (search) | Assistant with web search | OpenAI index (OAI-SearchBot) | No publisher report |
| Perplexity | Answer engine, sources displayed | Perplexity index (PerplexityBot) | Visible sources, manual check |
| Microsoft Copilot | Assistant backed by Bing | Bing index (Bingbot) | Citations in Bing Webmaster Tools |
| Gemini, Claude | Assistants with web search | Google for Gemini; Claude’s own web search | No publisher report |
In terms of usage, the ranking moves fast. At the end of May 2026, ChatGPT accounted for 46.4% of the assistant market, compared with more than 50% until January. Gemini reached 27.7% and Claude 10.3%, with the others staying below 5% (TechCrunch, based on Sensor Tower, June 16, 2026). These figures measure app usage worldwide. No public measurement gives market shares in France.
Google introduced AI Mode on March 5, 2025 and rolled it out in France together with AI Overviews on July 22, 2026. The details of these two surfaces are on our pages about Google’s AI Overviews and Google AI Mode.
How does an AI search engine build its answer?
A language model answers from two reserves. The first is its training knowledge, frozen at a given date. The second is on-the-fly search, also called grounding. The engine then queries a web index and reads the selected pages. A little-known brand depends almost entirely on the second.
- Interpretation: the engine rephrases the intent behind the question.
- Searches: it runs several related queries. Google calls this process query fan-out. For AI Mode, it describes it as simultaneous searches on subtopics and several data sources (Google, March 5, 2025).
- Retrieval: it selects pages from its index.
- Sorting: it isolates the useful passages and ranks them.
- Writing: it writes the answer and attributes, or does not attribute, some sources.
The consequence for a website: a passage gets picked up if it answers a specific question on its own, with verifiable facts. The approach is detailed in our GEO optimization method.
Where do the sources cited by each engine come from?
Each AI engine vendor crawls the web with its own crawlers. Their documentation clearly states which one is used for citation.
- OpenAI: OAI-SearchBot is used to surface websites in ChatGPT’s search results. A site that blocks it no longer appears in these answers, except possibly as a navigation link. GPTBot, for its part, collects data for model training (OpenAI, crawler documentation).
- Perplexity: PerplexityBot surfaces websites in the results and is not used to train models. Perplexity-User acts at a user’s request and generally ignores robots.txt (Perplexity, crawler documentation).
- Anthropic: Claude has been searching the web since March 20, 2025, on all plans since May 27, 2025. Its answers cite their sources directly (Anthropic, March 20, 2025).
- Google and Microsoft: AI Overviews and AI Mode draw on Google’s index, Copilot on Bing’s. Being well crawled by Googlebot and Bingbot remains the foundation.
The engines do not rely on the same types of sites either. Semrush analyzed 126 million prompts between January and April 2026. ChatGPT relies heavily on Reddit and Wikipedia, Gemini on Wikipedia, Reddit and YouTube (Semrush, June 26, 2026). A brand absent from these spaces is less likely to be cited, even with a good website.
Warning
A properly configured robots.txt is not enough: a firewall or a CDN can block these crawlers without any explicit decision. Check the actual access in your server logs. The steps to follow are on our page about GPTBot and AI crawlers.
The case of ChatGPT, the most requested, is covered separately on our page about ChatGPT SEO.
What is the best AI search engine?
There is no best engine in absolute terms. The right choice depends on the use. A website publisher does not have to choose anyway: its customers use several engines at once.
| Need | Suitable engine | Why |
|---|---|---|
| Check every claim | Perplexity | Sources displayed throughout the answer |
| Keep your usual search habits | Google AI Overviews and AI Mode | Built into Google Search |
| Hold a long conversation, write | ChatGPT, Claude, Gemini | Full assistants that trigger a web search when needed |
| Work in the Microsoft environment | Copilot | Backed by Bing and Microsoft tools |
For a marketing manager, the right question is the reverse: on which engines do your customers ask their questions, and does your brand appear there?
What can a website publisher measure on these engines?
Measurement remains partial and uneven across engines.
- Google: since August 31, 2026, Search Console shows, for all sites, the impressions earned in AI Overviews and AI Mode, by page. It does not give clicks (Google Search Central Blog, June 3, 2026).
- Microsoft: the Bing Webmaster Tools AI Performance report has been in preview since February 10, 2026 (Bing Webmaster Blog, February 10, 2026). It shows citations in Copilot and Bing’s AI summaries, the pages cited and the queries the AI used to find the content.
- ChatGPT, Perplexity, Gemini, Claude: no publisher report. You need to record a panel of questions at fixed intervals and track referral traffic in your analytics tool.
An AI search engine does not give the same answer twice: only draw conclusions from repeated measurements. The full method is described on our page about measuring AI visibility. The difference with classic search engine optimization is covered in GEO vs SEO.
Frequently asked questions
What is the best free AI search engine?
ChatGPT, Perplexity, Gemini, Copilot and Claude all offer a free version with web search. Google’s AI Overviews are built into classic search. Perplexity stands out by always displaying its sources; the best choice depends on the use.
Which AIs are the most used?
According to Sensor Tower, at the end of May 2026, ChatGPT accounted for 46.4% of the AI assistant market, Gemini 27.7% and Claude 10.3%. Grok, Perplexity, DeepSeek and Meta AI each stayed below 5%. These shares cover app usage worldwide.
Is there a French AI search engine?
Yes: Le Chat, the assistant from the French company Mistral AI, runs web searches. However, no public measurement makes it possible to assess its share of usage in France.
Does an AI search engine replace Google?
Not for now: Google has built its own AI answers into its engine, and the assistants themselves rely on search indexes. For a website, being well indexed by Google and Bing remains the condition for being cited.
Sources
- TechCrunch, ChatGPT’s market share slips below 50% for the first time (Sensor Tower data), published on June 16, 2026. Accessed on September 24, 2026.
- Google, Expanding AI Overviews and introducing AI Mode, published on March 5, 2025. Accessed on September 24, 2026.
- OpenAI, Overview of OpenAI Crawlers, documentation. Accessed on September 24, 2026.
- Perplexity, Perplexity Crawlers, documentation. Accessed on September 24, 2026.
- Anthropic, Claude can now search the web, published on March 20, 2025, updated on May 27, 2025. Accessed on September 24, 2026.
- Semrush, 2026 AI Visibility Index, published on June 26, 2026. Accessed on September 24, 2026.
- Google Search Central Blog, Introducing Search Generative AI performance reports in Search Console, published on June 3, 2026, note of August 31, 2026. Accessed on September 24, 2026.
- Bing Webmaster Blog, Introducing AI Performance in Bing Webmaster Tools Public Preview, published on February 10, 2026. Accessed on September 24, 2026.
