Which AI search engine has the most users?

Google AI Overviews reaches the most users because it is built into Google Search, which processes over 8.5 billion queries per day. As a standalone AI search product, ChatGPT has the largest user base with over 400 million weekly active users. Perplexity AI is the largest purpose-built answer engine with over 100 million weekly queries.

Which AI search engine is best for getting your startup cited?

Perplexity AI is often the easiest entry point because it prioritizes content quality over domain authority and provides transparent inline citations. ChatGPT Search and Google AI Overviews also cite smaller brands, but tend to weight established authority signals more heavily.

Do you need to optimize differently for each AI search engine?

The core optimization principles are the same across all AI search engines: structured content, definition-first paragraphs, cited statistics, and strong E-E-A-T signals. The main difference is technical - each platform has its own web crawler that you need to allow in your robots.txt file.

What are the best tools for tracking AI search visibility?

Otterly.ai tracks brand mentions and citations across multiple AI search engines. Peec AI monitors AI-generated answers for your target keywords. Both provide dashboards showing when and where your content gets cited. For manual tracking, run your target queries in each AI search tool and document which sources get cited.

Top AI Search Engines Compared in 2026

AI search engines are tools that use large language models to search the web, read content from multiple sources, and generate direct answers with source citations instead of returning a traditional list of links. The major AI search engines in 2026 include Google AI Overviews, ChatGPT Search, Perplexity AI, and Microsoft Copilot - each with different strengths, user bases, and implications for content creators and startups.

The Major AI Search Engines

Google AI Overviews

Google AI Overviews are AI-generated summaries powered by Google's Gemini model that appear at the top of Google search results. They launched in May 2024 in the US and have expanded to over 100 countries.

Reach: Built into Google Search (8.5B+ daily queries)
Citation style: Small website chips within the generated text
Source selection: Heavily weighted toward pages already ranking well organically
Crawler: Googlebot (same as traditional Google Search)
Best for: Reaching the broadest possible audience through existing search behavior

ChatGPT Search

ChatGPT Search is OpenAI's web search feature integrated into ChatGPT, enabling real-time web browsing with source citations. It evolved from the SearchGPT prototype.

Reach: Over 500 million weekly active users on ChatGPT
Citation style: Source links at the bottom of responses, sometimes inline
Source selection: Reads full page content; values clarity, authority, and freshness
Crawler: OAI-SearchBot / GPTBot
Best for: Complex, research-oriented queries where users want synthesized answers

Perplexity AI

Perplexity AI is a purpose-built answer engine with inline numbered citations as a core feature. Founded in 2022, it processes over 100 million weekly queries.

Reach: Over 100 million weekly queries, growing rapidly
Citation style: Inline numbered citations [1], [2], [3] within the text
Source selection: Prioritizes content quality and specificity; lower domain authority threshold
Crawler: PerplexityBot
Best for: Startups seeking AI search visibility - most transparent citations, lowest barrier to entry

Microsoft Copilot

Microsoft Copilot integrates AI search into Bing, Windows, Office, and Edge. Powered by OpenAI's models with Bing's search index, it reaches users across Microsoft's product ecosystem.

Reach: Hundreds of millions through Windows, Edge, and Office integration
Citation style: Numbered footnotes with source links
Source selection: Uses Bing's search index plus AI model evaluation
Crawler: Bingbot
Best for: Reaching users in enterprise and productivity contexts

Feature Comparison

Feature	Google AI Overviews	ChatGPT Search	Perplexity AI	Microsoft Copilot
Launch	May 2024	Late 2024	2022	2023
User base	8.5B+ daily search queries	500M+ weekly users	100M+ weekly queries	100M+ via Microsoft products
Always searches web	Only for some queries	When triggered	Yes, always	When triggered
Citation transparency	Medium	Medium	High	Medium
Follow-up questions	Limited	Full conversational	Full conversational	Full conversational
Ad-supported	Yes (alongside results)	Not yet	Introduced late 2024	Yes
Free tier	Yes	Yes	Yes	Yes
Enterprise offering	Google Workspace	ChatGPT Enterprise	Perplexity Enterprise Pro	Microsoft 365 Copilot

How Do AI Search Engines Select Sources?

Despite their differences, all AI search engines share common principles for selecting which content to cite:

Content clarity and structure. All AI models perform better when extracting from well-structured content with clear headings, definition-first paragraphs, and concise explanations. The Princeton GEO research found that structured content with statistics and citations saw up to 40% higher visibility in AI-generated responses.

Authority signals. Every AI search engine weighs some form of authority - domain reputation, author credentials, backlinks, and cross-web mentions. Google weights traditional SEO authority most heavily. Perplexity is more open to newer, less established sources.

Content freshness. All platforms prefer recent content with current data. Publishing dates, "last updated" timestamps, and recent statistics signal that your content is current and maintained.

Topical depth. AI models prefer dedicated, in-depth pages over pages that briefly mention a topic among many others. A page entirely about "LinkedIn algorithm 2026" will outperform a generic "social media tips" page for that query.

Managing AI Crawlers

Each AI search engine uses its own web crawler. To appear in their results, you need to allow these crawlers in your robots.txt:

Googlebot - Google (AI Overviews and traditional search)
GPTBot / OAI-SearchBot - OpenAI (ChatGPT Search)
PerplexityBot - Perplexity AI
Bingbot - Microsoft (Copilot and Bing)

Blocking any of these crawlers means your content will not appear in that platform's AI-generated answers. Some publishers block AI crawlers for copyright reasons, but if you want AI search visibility, you need to allow them.

Which AI Search Engine Should Startups Focus On?

The answer is all of them - because the optimization strategies overlap almost entirely. Writing clear, structured, authoritative content with cited statistics gets you visibility across every AI search engine simultaneously.

That said, if you need to prioritize:

Start with Perplexity - Lowest barrier to citation, most transparent attribution, easiest to track
Optimize for Google AI Overviews - Largest reach, builds on existing SEO investment
Ensure ChatGPT Search compatibility - Growing fastest in user adoption, valuable for complex queries
Allow Microsoft Copilot crawling - Free incremental visibility through Bing

The tools for monitoring your AI search visibility include Otterly.ai for tracking brand mentions across AI search engines, Peec AI for monitoring AI-generated answers for your target keywords, and manual testing by running your target queries across each platform. The startups that build AI search optimization into their content strategy now will compound their visibility advantage as AI search usage continues to grow.