For two decades, "search" meant one thing for most businesses: a list of ten blue links on Google. In 2026 that picture is far more crowded. Your customers now ask questions in Google's AI Mode, in ChatGPT, in Perplexity, in Microsoft Copilot, in Claude and in a growing list of smaller tools. Each one reads the web differently, cites sources differently and sends traffic back in different amounts.
That does not mean classic SEO is dead. Most AI search engines still lean heavily on traditional web indexes, and the brands that show up in AI answers are usually the ones that already have crawlable, trustworthy, well-linked content. What has changed is the number of doors a customer can walk through before they reach you.
This guide explains how the main AI search engines work, where they get their information, which crawlers you need to allow, and how to prioritise your effort without spreading your team too thin.
Key Takeaways
- AI search engines combine a large language model with a live web index, so being crawlable and indexable is still the entry ticket.
- Google AI Mode and AI Overviews use your normal Google index; Google says there are no extra technical requirements beyond being indexed and snippet-eligible.
- ChatGPT, Claude and Perplexity each use their own search crawlers, which are separate from their model-training crawlers. Block the wrong one and you can disappear from answers.
- Third-party mentions on forums, review sites, video platforms and reference sites shape what AI tools say about you, not just your own pages.
- Measure AI visibility separately: referral traffic in GA4, citations by platform and brand-mention accuracy.
What is an AI search engine?
An AI search engine is a tool that answers a question in natural language instead of (or as well as) returning a list of links. Behind the scenes it usually does three things: it interprets the question, it runs one or more searches against a web index, and it asks a language model to write an answer grounded in the pages it retrieved, often with citations.
Google calls the multi-search step "query fan-out". Its documentation describes AI Mode and AI Overviews as potentially "issuing multiple related searches across subtopics and data sources" before composing a response. Other platforms work in a similar way, even if they name it differently. If you want the deeper mechanics, our explainer on agentic search covers how AI systems plan and run multi-step searches.
The practical consequence is that one customer question can trigger many sub-queries. A page that answers one specific sub-question clearly can be cited even if it would never rank first for the head term.
The main AI search engines in 2026
The list below focuses on the tools that matter most for marketing visibility. It is not a ranking of "best" tools; it is a map of where your customers are likely to meet your brand.
| Platform | How it finds sources | Crawler(s) to know | What it means for you |
|---|---|---|---|
| Google AI Overviews and AI Mode | Google's own search index plus query fan-out | Googlebot (Google-Extended controls Gemini training only) | Standard Google SEO applies; pages must be indexed and snippet-eligible |
| ChatGPT search | OpenAI's search index and live fetching | OAI-SearchBot (search), ChatGPT-User (user actions), GPTBot (training) | Allow OAI-SearchBot if you want to appear in ChatGPT answers |
| Perplexity | Its own index plus on-demand page visits | PerplexityBot (search), Perplexity-User (user requests) | Fresh, well-structured pages with clear facts are cited often |
| Microsoft Copilot | Bing's index | Bingbot | Bing Webmaster Tools and IndexNow help new pages get found quickly |
| Claude | Web search tool with Brave Search listed as a provider | Claude-SearchBot, Claude-User, ClaudeBot (training) | Visibility in Brave's index and allowing Anthropic's search agents both matter |
Google AI Overviews and AI Mode
Google announced on 20 May 2025 that AI Mode was rolling out to everyone in the US without a Labs sign-up, describing it as the place where it would first bring Gemini's newest capabilities. AI Overviews appear above regular results; AI Mode is a separate, conversational tab. Both draw on the same index you already optimise for.
“There are no additional requirements to appear in AI Overviews or AI Mode, nor other special optimizations necessary.”
— Google Search Central, AI features and your website
That is reassuring, but "no special optimisation" is not the same as "no work". Pages still have to be indexed, eligible for a snippet, and genuinely useful. Our guides to Google AI Mode goes into the details.
ChatGPT search
OpenAI introduced ChatGPT search on 31 October 2024 and, by February 2025, had made it available to everyone where ChatGPT is offered, without a sign-up. Answers include a Sources panel. OpenAI's crawler documentation is explicit that its search crawler and training crawler are different: OAI-SearchBot is "used to surface websites in search results in ChatGPT's search features," while disallowing GPTBot signals that content should not be used for training. See our ChatGPT search optimisation guide for platform-specific tactics.
Perplexity
Perplexity positions itself as an "answer engine" and shows citations prominently. Its documentation says PerplexityBot is designed to surface and link websites in search results and is not used for foundation-model training, while Perplexity-User fetches pages when a person asks a question. Our Perplexity SEO guide covers how to appear there.
Microsoft Copilot
Copilot is grounded in Bing. That makes Bing Webmaster Tools worth setting up even if Bing sends you little classic traffic. IndexNow, which is supported by Microsoft Bing, Naver, Seznam.cz, Yandex and Yep, lets you notify participating engines when a URL changes.
Claude and other assistants
Anthropic added web search to Claude in March 2025, with citations to its sources. Its subprocessor list names Brave Search under web search, which is why Brave visibility matters. We cover this in detail in how to get your brand mentioned by Claude. Semrush's September 2026 roundup of AI search tools also includes Brave Leo, Duck.ai, Consensus (for academic research) and DeepSeek, which shows how fragmented the space has become.
How AI search engines choose what to cite
No platform publishes its full citation logic, so be wary of anyone who claims to know "the algorithm". What we can say from official documentation and repeatable observation is that AI engines tend to cite pages that:
- are accessible to their search crawler and return a normal 200 status;
- answer a specific sub-question directly, near the top of a section;
- contain facts that are easy to verify, such as dates, names, prices or steps;
- come from sources that other trusted sites reference and link to;
- are current, especially for fast-moving topics.
Our article on how AI chooses sources unpacks these signals, and third-party citations in AI explains why reviews, forums and directories carry so much weight.
Third-party sources are a big part of the picture. Semrush's study of more than 230,000 prompts between July and October 2025 found that the share of ChatGPT responses citing Reddit or Wikipedia swung dramatically over just a few weeks. The lesson is not to chase one domain, but to make sure accurate information about you exists in several trusted places.
A step-by-step plan to get visible in AI search
- Audit crawler access. Check robots.txt, your CDN and your firewall for blocks on Googlebot, Bingbot, OAI-SearchBot, PerplexityBot and Claude-SearchBot. Our guide to AI crawlers shows what each one does.
- Fix the fundamentals. Make sure key pages are indexed in Google and Bing, load quickly and render without relying on fragile JavaScript.
- Map customer questions. List the questions buyers ask before choosing you, including comparison and "best for" questions.
- Write answer-first sections. Give each question a clear heading and a direct answer, then supporting detail.
- Strengthen your entity. Keep your name, address, descriptions and profiles consistent across your site, Google Business Profile, LinkedIn and industry directories.
- Earn third-party mentions. Reviews, expert quotes, podcasts and genuine community participation all feed AI answers.
- Measure and iterate. Track AI referrals and test your key prompts monthly.
Measuring AI search performance
Traffic from AI Overviews and AI Mode is counted inside Google Search Console's Performance report, mixed with regular web search. Other AI platforms show up as referrals. Our guide to tracking AI traffic in GA4 shows how to build a channel group for them.
| Metric | Where to find it | Why it matters |
|---|---|---|
| AI referral sessions | GA4 custom channel group (chatgpt.com, perplexity.ai, copilot.microsoft.com, claude.ai, gemini.google.com) | Shows which platforms actually send visitors |
| Key events from AI referrals | GA4 conversions by channel | Tells you whether AI visitors convert |
| Brand citation rate | Manual prompt testing or an AI visibility tool | Shows how often you are named or linked for priority questions |
| Answer accuracy | Prompt testing log | Catches outdated prices, wrong locations or confused competitors |
| Google impressions and clicks | Search Console Performance report | Includes AI Overviews and AI Mode traffic alongside web results |
If clicks are falling while impressions hold steady, read our analysis of AI traffic loss before you change strategy.
Common mistakes
- Blocking every AI bot by reflex. Blocking a training crawler like GPTBot is a business decision; blocking a search crawler like OAI-SearchBot removes you from answers.
- Chasing a single platform. Usage is split. A strategy that only targets ChatGPT ignores Google AI Mode and Copilot users.
- Buying "AI ranking" hacks. Hidden prompts, keyword-stuffed FAQ blocks and fake reviews risk spam penalties and rarely work for long.
- Ignoring Bing. Copilot depends on Bing's index, and several other tools use Bing data too.
- Not checking what AI says about you. Wrong facts spread. Test your brand name and core questions regularly.
Related Guides
- WebMCP Explained: Making Your Site Usable by AI Agents
- Reddit and AI Search: Why Forum Mentions Shape AI Answers
- Video and AI Search: Getting YouTube Content Cited by AI
Frequently Asked Questions
What is the most used AI search engine?
Usage figures change quickly and are often self-reported by vendors. Google's AI Overviews reach the most people because they appear inside normal Google results, while ChatGPT is the most popular standalone assistant. Check current, dated sources before quoting numbers.
Do I need separate SEO for each AI search engine?
Mostly no. The same foundations, crawlable pages, clear answers and trusted mentions, work across platforms. The main platform-specific tasks are crawler access, Bing indexing for Copilot and checking how each tool describes your brand.
Does blocking GPTBot remove my site from ChatGPT search?
No. According to OpenAI's documentation, GPTBot is for model training and OAI-SearchBot is for search. To appear in ChatGPT search results you need to allow OAI-SearchBot.
Is llms.txt required for AI search engines?
No major AI search engine requires it. Google says there are no special requirements for AI Overviews or AI Mode. An llms.txt file is optional and experimental.
How do I know if AI search engines send me traffic?
Create a custom channel group in GA4 that matches AI referrers such as chatgpt.com and perplexity.ai, and review Search Console for Google AI features traffic, which is included in the Performance report.
Conclusion
AI search engines have multiplied the places where customers form opinions about your brand, but the playbook is less mysterious than it looks: be crawlable, be clear, be cited by others and measure what happens. Start with a crawler audit and a list of the questions your buyers really ask, then build from there.
If you want help building visibility across Google, ChatGPT, Perplexity and Copilot, our SEO services team includes generative engine optimisation in every strategy. Get a quote and we will audit where your brand stands today.
References
- Google Search Central: AI features and your website
- Google: AI Mode update (May 2025)
- OpenAI: Introducing ChatGPT search
- OpenAI: Overview of OpenAI crawlers
- Perplexity: Perplexity crawlers
- Anthropic: Does Anthropic crawl data from the web?
- Semrush: 9 best AI search engines in 2026
- Semrush: The most-cited domains in AI
