Answer engine optimization · Research
Do ChatGPT and Gemini use the same sources?
We put the same 8 queries, the kind a worried business owner punches into a search bar, to both ChatGPT and Gemini. Between them, the two AI engines served up 134 source mentions from 129 different domains. Only 5 of those domains were cited by both.
This isn't some minor disagreement in a forgotten corner of AI search. Those 8 questions are the exact queries an anxious owner fires off when they think something's broken: "why is my business not showing up on ChatGPT," "my competitor shows up in ChatGPT but I don't," "how to get my business recommended by ChatGPT," "is SEO dead or evolving in 2026." If you'd expect any topic to force the big AI engines to agree on a few core, authoritative pages, you'd think it would be a topic about the engines themselves.
They didn't agree. For 7 of the 8 questions, ChatGPT and Gemini cited zero of the same domains. The one question where they overlapped even a little, "how do I check if my business appears in AI search results," shared exactly two domains: Reddit and a competing visibility checker called SearchScore. Every other source was unique to one engine or the other.
How we ran it
We already had a script from our own probe work back in August that sends owner-anxiety questions through the OpenAI API with web search enabled and logs every cited domain. This month, we built a parallel version for Gemini, using Google's search grounding, and aimed it at the exact same 8 questions. ChatGPT's run returned 47 unique domains across its 8 answers. Gemini's run, which happened two weeks later, returned 87.
Two engines, two different worlds of sources
The two pools of sources hardly overlap at all. ChatGPT's answers rely on a swarm of small, similarly-named AI-visibility startups: fonzy.ai, scanmygeo.com, sofind.ai, peekl.io, rankley.com, aisearchgap.com, answerlift.ai, mentionsonai.com. Look at that list and you'll spot a trend: a whole wave of tiny new products has emerged to answer the very question we were asking, and ChatGPT is citing them almost to the exclusion of any deep industry research or a major publisher.
Gemini's answers point in a completely different direction. Its citations favor established marketing agencies and SEO publishers: The HOTH, Entrepreneur, HubSpot, SEMrush, Search Engine Journal, Search Engine Land. It also has its own distinct cluster of visibility-checker startups, ones ChatGPT never once mentioned: fixaeo.com, honeyb.ai, rankscope.ai, wonderchat.io, limy.ai. You have two different engines, asked about the same new tool category, and each has essentially found a completely different set of tools. This even applies to the single point of overlap. SearchScore, the shared domain in the "how do I check" answer, wasn't a media outlet or a research page. It was another company doing basically what we do here at askchat.studio, appearing as a citation in both engines while we, still in the middle of building our own probe, were nowhere to be found in either.
What this comparison is and isn't
Let's be clear about what this comparison represents. The ChatGPT data is from an API call on August 27; the Gemini data is from a separate call two weeks later on September 10. So this is a look at two different days rather than a single, simultaneous snapshot. Gemini's search grounding is also inconsistent on repeat runs: asking the identical question three times in a row might get you 18 sources, then 14, then zero, because the model sometimes pulls from memory rather than kicking off a fresh search each time. So, no, this isn't a lab-controlled, captured-at-the-same-moment study.
What it does show, however, fits a pattern we noticed last month when we compared ChatGPT's API to its live browser interface on three owner questions: there were zero shared domains there, too. Different entry point, different engine, same outcome. The sources an AI shows you seem to depend more on which door you used to get in than on the actual question you asked.
For what it's worth, neither engine cited askchat.studio. We're too new for that, and we're not pretending otherwise.
What it means if you own a local business
There isn't one single "get cited by AI" task you can complete. If your business gets named when someone asks ChatGPT about it, that tells you absolutely nothing about whether Gemini would name you for that same question. That's because the two engines are pulling from source pools that barely intersect. A business that's highly visible in one engine's answers could be completely invisible in another's, even if nothing about the business itself has changed, simply because that engine went looking in a different place.
This also changes the meaning of "checking your visibility." A single test on a single engine only tells you about that engine, and almost nothing about AI search in general. A worried owner might check ChatGPT once, get a good result, and stop, but they still have no idea what Gemini, Perplexity, or Claude would tell that same customer if they asked the same question five minutes later on a different app. Treating "AI search" as a single channel to optimize is like treating several completely separate audiences as one.
The solution isn't complex, it's just not very flashy: you have to check more than one engine, and you have to check them more than once. A single positive result from a single tool is just a snapshot of one door on one day. It's not the whole building.
Sources: OpenAI API with web search, 8 owner-anxiety queries, August 27, 2026. Gemini API with Google Search grounding, same 8 queries, September 10, 2026. Domain lists and overlap counted directly from citation logs.