Why AI Engines Disagree: ChatGPT vs Gemini vs Google AI Overviews on the Same Question

AI engines disagree less about who the leaders are than about everything around them. In our September probe, ChatGPT, Gemini and Google AI Overviews shared 3 to 5 of their top five brands in every industry we tested. Where they split was on the brands below the leaders, on how often they named brands at all, and above all on which sources they cited. That is why a brand can look strong on one engine and invisible on another, and why AI visibility has to be measured engine by engine.

The setup

To pick the first industries for the AI Citation Index, we asked the same buyer questions on three engines:

• 56 questions, 8 per industry, across 7 industries: help desk software, email marketing software, project management software, personal loans, cruise lines, small business insurance, and proxy and web data.
• 3 runs of each question between September 30 and October 1, 2026, in US English, logged out.
• Engines: Google AI Overviews, Gemini and ChatGPT in search mode, collected with the Ujeebu API.
• 406 answers in total: 168 each from Google AI Overviews and ChatGPT, 70 from Gemini (it failed often in this window, so its numbers are thin).

The sample is small. Read what follows as patterns to test in your own category, not as market statistics. The methodology explains how the weekly index measures the same things at a larger scale.

Where the engines agree: the leaders

For each industry we compared each engine's five most named brands. The overlap was high everywhere:

In personal loans, all three engines had the same five lenders in their top five. In project management, the same five tools. The categories with the most disagreement at the top were help desk software and proxy and web data, both crowded markets with many similar products.

So if you are a category leader, you will probably show up on every engine. The disagreement is a problem for everyone else.

Where they split, part 1: the runners-up

Below the leaders, the lists diverge. In help desk software, ChatGPT named 20 distinct brands across its answers, Google AI Overviews 16 and Gemini 15. A brand ranked sixth or eighth on one engine can be missing entirely from another engine's answers to the same questions.

Answer length differs too. In help desk software, Gemini named a median of 6 brands per answer, ChatGPT 5 and Google AI Overviews 4. A longer list gives challengers more room. A shorter list is a tougher cut.

For a mid-sized brand, this is the practical consequence: your visibility is not one number. You can be a regular on one engine and an occasional name on another, for the same buyer question.

Where they split, part 2: whether to name brands at all

Engines also differ in how willing they are to recommend specific brands. We measured the share of answers that named at least three brands:

ChatGPT was the most reserved in most industries. It more often answered with a short comparison of two options, a how-to, or a question back to the user. In one small business insurance answer, it only asked a clarifying question. Its hedge rate (answers with no brand, or very few brands plus advice like "rates vary") reached 12% in email marketing and in proxy and web data, against 4% or less for Google AI Overviews in those industries.

In regulated categories like loans and insurance, that caution shows up clearly. For brands, it means a ChatGPT answer is less often a list you can climb, and more often a short answer you are either in or out of.

Where they split, part 3: the sources

This is the largest difference. The share of citations that went to third-party sites (not the brands' own websites) was:

• ChatGPT: 6% to 48% depending on the industry. It mostly linked the sites of the brands it recommended.
• Google AI Overviews: 56% to 90%. YouTube and Reddit were among its most cited domains in most industries, and finance publishers led in personal loans.
• Gemini: 50% to 97%, spread across many small blogs and review sites.

ChatGPT's citations were also concentrated: its five most cited domains held 57% to 88% of its citations per industry. Google AI Overviews and Gemini spread theirs more widely.

The same question, then, can lead a buyer to a vendor pricing page on ChatGPT, a YouTube review on Google AI Overviews and a niche comparison blog on Gemini. We cover the source data in more detail in which sources AI answers cite.

Why this happens

We can describe what the engines did; we cannot see inside them. But the patterns fit how they are built:

1. Different retrieval. Each engine runs its own search step and reads different pages before writing. Google AI Overviews sits inside Google Search results, which include video and forum results. Gemini also comes from Google, yet in our data it cited very different pages from Google AI Overviews. ChatGPT runs its own search step.
2. Different source preferences. The citation data suggests different preferences: ChatGPT links primary sources such as vendor pages, Google AI Overviews leans on popular community and publisher pages, Gemini reaches deeper into the long tail.
3. Different caution settings. Engines are tuned differently for advice in areas like money and insurance, which affects how readily they name brands.
4. Run-to-run variation. Every engine varies between runs. In our probe the overlap of brand sets between runs of the same question averaged 0.6 to 1.0 per engine and industry. Some disagreement between engines is just that noise, which is why one answer per engine proves little.

There is also a measurement caveat: each engine returns its answer in a different format. We fixed the formatting differences we found, but part of any cross-engine difference can still come from how answers are collected and read.

What this means for your brand

• Measure each engine separately. An average across engines hides the most useful finding: where you are missing. The AI Citation Index reports every engine on its own for this reason.
• Fix sources per engine. For ChatGPT, make your own pages answer buyer questions directly. For Google AI Overviews, be present in the videos, threads and publishers it cites. For Gemini, watch the comparison content in your niche.
• Track the runners-up, not just the leader. If you are not a category leader, your fight is for places four to eight, and that is exactly where the engines disagree.
• Use repeated runs. Ask every question several times before drawing a conclusion. Our brand snapshots ask each prompt three times on each engine.

To see how the engines treat your own brand, start with the free AI answers check: 10 buyer questions per engine, your brand next to one competitor. If you want to run the comparison yourself, the ChatGPT, Gemini and SERP APIs return answers and citations as JSON. Our other datasets are on Ujeebu Data.

FAQ

Why do ChatGPT and Gemini give different answers?

They search different parts of the web, prefer different sources and are tuned differently. In our probe they agreed on most leaders in each industry but differed on lower-ranked brands and, most of all, on the sites they cited.

Do ChatGPT and Google AI Overviews recommend the same brands?

Mostly at the top. Their top-five brands overlapped by 4 or 5 of 5 in every industry we tested. Below the top five the lists diverged.

Which AI engine cites brand websites the most?

ChatGPT, by a wide margin in our data. Between 52% and 94% of its citations went to the recommended brands' own sites, depending on the industry. Google AI Overviews and Gemini cited mostly third-party pages.

Which engine is most cautious about recommending brands?

ChatGPT, in most industries we tested. It named three or more brands less often than Google AI Overviews or Gemini, especially in personal loans and small business insurance.

Should I optimize for one AI engine or all of them?

Start with the engines your buyers use, but measure all of them. Being recommended by one engine does not mean you appear on the others, and the fixes differ by engine.

How large was this study?

Small: 56 buyer questions across 7 industries, asked 3 times, for 406 answers on ChatGPT, Gemini and Google AI Overviews. The weekly AI Citation Index asks 200 questions per industry.