Which search engine powers each AI assistant?

Every major AI assistant answers questions by searching the web, but none of them search the same web. ChatGPT runs on Bing, though OpenAI has said in court it wants its own index to take over most of that work. Claude runs on Brave Search. Gemini and Google's AI Overviews run on Google's own index. Perplexity started out on Bing, then spent three years building a crawler and index of its own that it now sells to other companies. Grok pulls live posts straight from X, which nobody else can touch, but xAI has never disclosed what powers the web half of its search.

That one paragraph is the answer most people are looking for. The rest of this post is the evidence, because the companies involved rarely announce any of it. Everything below comes from vendor documentation, official disclosures, court testimony, or independent tests, with the source named as each claim comes up.

The short answer, in one table

AI engine	Search backend	Status of the evidence
ChatGPT (OpenAI)	Bing + Shopify for products	Confirmed by OpenAI; a first-party index is a stated goal in sworn testimony
Claude (Anthropic)	Brave Search API	Confirmed via Anthropic's official subprocessor list
Gemini (Google)	Google Search	Confirmed in Google's docs
AI Overviews / AI Mode	Google Search index with query fan-out	Confirmed in Google's docs
Perplexity	Its own first-party index, with third-party supplements	Confirmed in Perplexity's own materials
Grok (xAI)	X posts (first-party) + an undisclosed web backend	Web half undisclosed

Two facts explain most of this table. Only Google and Microsoft own web-scale crawling infrastructure, built over decades, so everyone else rents an index, scrapes one, or builds their own. And Microsoft retired its public Bing Search APIs on August 11, 2025, which pushed the rest of the market toward Brave, scraping services, and first-party crawlers.

What search engine does ChatGPT use?

ChatGPT uses Microsoft Bing as its contracted search provider, and OpenAI's help center names exactly two third-party providers: Bing and Shopify. Shopify was added to that list on May 15, 2025 and powers the product results behind ChatGPT's shopping features.

OpenAI doesn't plan to stay on Bing forever, and has said as much on the record. At the Google antitrust remedies trial in April 2025, ChatGPT lead Nick Turley testified under oath that OpenAI had "significant quality issues" with its existing provider, that Google had refused OpenAI's request for Search API access in 2024, and that OpenAI's goal is for its own index to eventually serve about 80% of ChatGPT search queries, a goal he called "years away." How far along that work is, OpenAI hasn't said publicly.

What search engine does Claude use?

Claude runs its web search on the Brave Search API. Anthropic disclosed this in its compliance paperwork rather than a press release: Brave Search sits on Anthropic's official subprocessor list, the public register of vendors that process data on its behalf, and was still listed there as of July 2026. Independent testing backs the disclosure up. Days after web search launched in March 2025, Simon Willison ran identical queries through Claude and through Brave Search directly and got matching citations on all ten results, and Claude's own web search tool definition contains a parameter named BraveSearchParams.

Brave Search is the largest independent web index outside Google and Microsoft: over 40 billion pages, built by Brave's own crawler plus anonymized signals from Brave browser users, fully independent of Bing since April 2023.

So why Brave? Anthropic has never explained the choice, but the options were thin. Google doesn't license its index as a raw API to anyone, and Microsoft was in the process of retiring the public Bing API in favour of a product costing 40% to 483% more. There's an ownership angle too: Google holds roughly 14% of Anthropic, so building Claude's search on Google would have meant depending on the company Claude competes with. Brave, independent and priced at $5 per thousand queries, avoided all of it.

Anthropic also documents a crawler called Claude-SearchBot that "navigates the web to improve search result quality," and added TurboPuffer, a search database, to its subprocessor list in May 2026.

Does Gemini use Google Search?

Yes. Gemini is the only major assistant with first-party access to the largest index on earth. Google's docs describe the flow plainly: the model decides whether a search would improve the answer, writes its own queries, gets results back from Google Search, and composes a response with citations mapped to source URLs.

AI Overviews and AI Mode pull from the same Googlebot-built index as the ten blue links, through the same ranking systems. The difference is the query pattern. Google calls it query fan-out: one question gets broken into subtopics and searched many times at once. A Google engineering director described AI Mode as "basically doing a dozen searches for you in the time it takes to do one."

The scale advantage is hard to overstate. Cloudflare measured Googlebot reaching roughly 70 to 700 times more unique pages than AI-only crawlers like GPTBot or ClaudeBot, partly because publishers can't block Googlebot without vanishing from search. Under pressure from the UK's competition regulator, Google shipped a Search Console toggle in June 2026 letting sites opt out of AI Overviews and AI Mode while staying in regular results. It's the first time that choice has existed.

Does Perplexity have its own search index?

Yes, and Perplexity is the inversion of everyone else on this list. ChatGPT, Claude, and Gemini are model companies that source search. Perplexity is a search company that sources models: its index stays constant while subscribers pick the LLM that sits on top.

It didn't start that way. At launch in December 2022, Perplexity was GPT-3.5 sitting on Bing results. Through 2023 it built its own crawler, indexer, and ranking stack, and by September 2025 the index had become a product in its own right, sold as a raw Search API positioned as a replacement for the retired Bing API.

The catch is how the content gets acquired. Cloudflare accused Perplexity in August 2025 of stealth crawling: an undeclared bot posing as Chrome, rotating IPs, fetching pages that were explicitly blocked in robots.txt. Perplexity disputes the attribution, and its stated doctrine is that a fetch made on behalf of a human user isn't crawling at all. News Corp, Britannica, and Reddit are testing that doctrine in court.

How does Grok search the web?

Grok's real advantage is data nobody else has: live X posts, queried through a first-party x_search tool. The web half is a black box. xAI publishes no crawler documentation and no user agent list, which makes it the only major operator whose retrieval stack is fully undisclosed. Any specific claim you read about Grok's web backend is speculation. If Grok visibility matters to you, an active and factual X presence is the one lever that's actually documented.

Why this matters if you run a website

Because these are separately built indexes with different crawl footprints, your brand can rank on page one of Google, which covers Gemini and AI Overviews, while being thin in Bing (ChatGPT's contracted layer) and completely absent from Brave (Claude's index). Each index draws its own picture of the web, and your brand looks different in every one.

Ranking and citation are also different games. One study found that top-ranked URLs matched what ChatGPT actually cited only about 7% of the time. Being retrievable and clearly quotable matters as much as position.

And the ground keeps moving. Shopify joined ChatGPT's provider list in May 2025. TurboPuffer appeared in Anthropic's stack in May 2026. Google shipped its opt-out toggle in June 2026. OpenAI has told a federal court it wants its own index to replace most of what Bing does for ChatGPT. What's true about your AI visibility this quarter may not be true next quarter.

The full research report behind this post, with source-by-source evidence grading, is available from Detectabli. If you want to know how your own brand actually shows up across most AI engines, we run a free visibility audit at detectabli.com.

Gabriel Lockstone is the founder of Detectabli, an AI visibility platform that measures how brands appear across AI engines.

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