There is no universal list of websites that dominate AI answers. Ahrefs’ September 2026 Brand Radar snapshots show six major generative-search surfaces building visibly different source ecosystems: YouTube leads Google AI Overviews, Reddit leads Google AI Mode, Gemini, ChatGPT and Perplexity, while Microsoft Copilot is topped not by a community or reference site but by Amazon.
The figures come from a series of Ahrefs studies updated on September 2, including its analyses of Google AI Overviews, Google AI Mode, Gemini, ChatGPT, Perplexity and Copilot. The data is proprietary Brand Radar measurement, not official provider telemetry, and it should not be read as a universal citation market share. Ahrefs says each article analyzes more than three million U.S. queries spanning all topics and reports a domain’s citation share among the top 50 sources in that engine’s measured dataset.
Within that methodology, however, the differences are large enough to undermine a common GEO shortcut: finding the domain that appears to be “best for AI citations” and optimizing around it across every platform. The source hierarchy changes materially depending on which answer engine is doing the retrieval.
YouTube leads AI Overviews, but loses the top spot in AI Mode
Google’s two generative Search experiences already demonstrate why platform-specific measurement matters. In Ahrefs’ September AI Overviews dataset, YouTube holds 22.9% of mention share among the top 50 sources, making it the leading domain. Reddit follows at 18.5%.
Move from AI Overviews to AI Mode and the order flips. Reddit leads at 17.9%, narrowly ahead of YouTube at 17.8%. Google itself appears third at 12.5%, followed by Facebook at 10.2% and Instagram at 5.7%.
The 0.1-point gap between Reddit and YouTube in AI Mode is too small to support a sweeping claim that one is structurally preferred over the other. What is more useful is the composition of the leading group. Google’s conversational Search surface gives substantial measured citation attention to community, video and social platforms rather than reproducing the same hierarchy as AI Overviews.
Gemini is the most Reddit-heavy of the six measured surfaces
Ahrefs finds an even more concentrated Reddit footprint in Gemini. Reddit accounts for 28.5% of mention share among the top 50 measured sources, roughly double YouTube’s 14.6%. Wikipedia follows at 8.8%, while Walmart appears at 2.8%.
That makes Gemini’s measured Reddit share substantially larger than Reddit’s corresponding share in AI Mode, ChatGPT or Perplexity. The finding is particularly interesting because Gemini and Google’s Search generative products belong to the same company yet do not produce identical domain distributions in Ahrefs’ datasets.
This is a reminder that “Google AI” is not one retrieval surface. Product context, query population, retrieval architecture, answer format and other implementation choices can change which sources ultimately receive citations. A strategy built from AI Overviews alone cannot simply be projected onto Gemini.
ChatGPT also puts Reddit first, but with a much flatter long tail
In Ahrefs’ September ChatGPT snapshot, Reddit leads with 16.8% mention share. Wikipedia is second at 7.0%, followed by Consumer Reports at 3.7%, Forbes at 3.1% and Engineer Fix at 2.8%.
The gap between Reddit and the next source remains large, but the rest of ChatGPT’s top group is less dominated by another social platform than the Google datasets. YouTube does not occupy the second position here, and the leading domains quickly diversify into reference, publishing, consumer-information and specialist sites.
That result should also be reconciled carefully with other recent measurements. NetContentSEO covered Promptwatch data showing a sharp August decline in Reddit citations inside its monitored ChatGPT Search sample. Ahrefs’ September snapshot still places Reddit first. The two findings are not necessarily contradictory because the vendors use different query sets, sampling systems, time windows and citation denominators.
The disagreement is itself useful. Citation percentages are measurements of a particular observation system, not permanent platform constants.
Perplexity gives Reddit and YouTube most of the top-source attention
Perplexity’s September distribution is unusually concentrated at the top. Reddit leads with 21.6% of mention share and YouTube follows at 20.8%. Wikipedia, in third place, drops to 6.3%.
Those first two domains therefore account for more than two-fifths of the mention share among Ahrefs’ top 50 Perplexity sources. Within this dataset, community discussion and video occupy a much larger combined footprint than any individual traditional publisher or reference source.
That does not mean a brand should move all of its GEO activity onto Reddit and YouTube. Ahrefs is measuring domain-level citation frequency across a broad query population. A company’s own relevant prompt universe may behave very differently, especially in specialist B2B, local, medical, financial or product categories.
NetContentSEO recently covered a useful counterexample: a B2B evaluation-stage dataset in which product pages captured 24.1% of citations, while Reddit, YouTube and discussion sources collectively accounted for only 4.2%. Query intent changes the source pool.
Copilot looks like a different retrieval economy
The sharpest break from the other engines appears in Microsoft Copilot. Amazon leads Ahrefs’ September dataset at 16.8%, followed by Walmart at 12.6%. Wikipedia is third at 7.6%, while additional commerce domains populate much of the top 20: Target, Etsy, Home Depot, Best Buy, Macy’s, Lowe’s and Wayfair all appear prominently.
YouTube, which leads AI Overviews and sits second in several other datasets, falls to 1.9% in Copilot. Reddit does not appear anywhere in Ahrefs’ Copilot top 50 for September.
The pattern makes Copilot look considerably more commerce-oriented than the other five measured surfaces. Ahrefs itself connects that distribution with Microsoft’s growing shopping and checkout capabilities. The data cannot establish that commerce functionality causes the source mix, but the contrast is striking: the leading domains are retailers rather than community platforms.
For ecommerce GEO, this means a Copilot strategy based on the source hierarchy observed in Gemini or Perplexity could miss the most visible domain class entirely. Retailer presence, marketplace listings and product-discovery surfaces may matter disproportionately in Microsoft’s measured ecosystem.
“Mention share” is not the share of every citation on the platform
The denominator is essential. Ahrefs defines mention share as a domain’s citations divided by the summed citations of the top 50 most-cited sources in the measured dataset. A 28.5% Gemini figure for Reddit therefore does not mean that 28.5% of every Gemini citation globally points to Reddit.
Nor do the datasets cover every country, language, user, topic or prompt. Ahrefs says the September snapshots use a large, search-backed set of real-user queries in the United States across all topics. That scale makes the results useful for mapping broad source patterns, but it does not turn them into universal market statistics.
The articles are also updated automatically each month using Ahrefs’ Agent A and Brand Radar data. The rankings should consequently be treated as monthly snapshots rather than fixed properties of the engines.
AI citation ecosystems can change without product announcements
That monthly framing matters because source behavior is volatile. NetContentSEO recently examined Goodie data reporting 16 changes in social citation mix across seven months, including several reversals. Those shifts were observed externally rather than announced by the AI providers.
Ahrefs’ September tables are therefore most valuable as a current map, not as a timeless rulebook. Reddit’s leadership across four engines may persist, increase or disappear as retrieval systems, licensing relationships, indexes, product interfaces and query populations evolve.
This volatility makes diversification more rational than chasing a single dominant intermediary. A brand that depends entirely on one community platform because it currently performs well in an AI citation study inherits the risk that the answer engine changes its retrieval behavior without warning.
The same domain can play different roles in different engines
Domain-level rankings also hide an important layer: why a source is being cited. Reddit can supply firsthand experiences, troubleshooting discussions, recommendations and long-tail opinions. YouTube can supply demonstrations, tutorials and creator explanations. Amazon and Walmart provide product inventory, specifications, pricing context and reviews. Wikipedia supplies broad reference material.
An answer engine does not necessarily “prefer” one domain in the abstract. Its measured source mix can emerge from the types of questions in the dataset and the retrieval value those domains provide for those questions.
That is why the practical GEO task is not to copy the top-domain chart. It is to understand what evidence formats an engine is repeatedly retrieving for the queries that matter to a business, then make authoritative information available in those formats and on properties the brand can realistically influence.
Reddit’s four-engine lead is important, but not a universal instruction
Reddit’s position deserves attention. It leads AI Mode at 17.9%, Gemini at 28.5%, ChatGPT at 16.8% and Perplexity at 21.6% in Ahrefs’ September data. Few individual domains achieve that level of cross-engine visibility.
The likely strategic lesson, however, is not “publish everything on Reddit.” Brands cannot fully control community discussion, and attempts to manufacture participation can undermine credibility. The more durable takeaway is that authentic experience, question-and-answer language, comparative discussion and user-generated evidence remain highly retrievable forms of content across several generative systems.
NetContentSEO explored some of those structural reasons earlier in our analysis of why Reddit appears so frequently in AI answers. The September Brand Radar data gives that broader pattern a current cross-engine measurement, while Copilot simultaneously demonstrates its limits.
Copilot breaks the idea of one GEO playbook
If every engine showed Reddit first and YouTube second, marketers could plausibly argue for a single cross-platform distribution recipe. Copilot prevents that conclusion. Its top two sources are Amazon and Walmart, while Reddit is absent from the top 50 and YouTube is far below its position on Google and Perplexity.
The implication is that source strategy should follow the target engine and query class. A consumer brand seeking visibility in Copilot may need to audit retailer product data and marketplace presence. A publisher targeting AI Overviews may need to understand why video receives such substantial citation attention. A company monitoring Gemini or Perplexity may need to pay closer attention to community evidence.
Even then, domain rankings should be the beginning of analysis rather than the final prescription. The relevant unit for a brand is not “all U.S. queries”; it is the subset of questions that can lead to discovery, evaluation or purchase in its own market.
GEO measurement needs an engine-by-engine source map
Ahrefs’ September dataset makes a strong case for abandoning aggregate “AI visibility” as the only metric. If different engines cite different ecosystems, combining them into one score can conceal the very differences that determine where a brand needs to invest.
A useful GEO dashboard should therefore preserve platform boundaries. Citation share in ChatGPT should not be treated as a proxy for Gemini. AI Overviews should not be assumed to behave like AI Mode simply because both are Google products. Copilot’s retailer-heavy source mix should not be averaged away inside a cross-engine score dominated by Reddit-heavy systems.
The same principle applies to experiments. A content or distribution change should be evaluated separately on the engines where it is expected to matter. Otherwise, a gain on one platform can be hidden by no movement on five others—or an apparent aggregate improvement can conceal a serious decline in the engine most important to the business.
The September map is a snapshot of six different evidence markets
The clearest conclusion from Ahrefs’ data is not that Reddit, YouTube or Amazon has “won” AI search. It is that each answer engine constructs a different evidence market. Google AI Overviews gives the largest measured share to YouTube. Four other surfaces put Reddit first. Copilot produces a source hierarchy dominated by retail.
Those differences exist even before marketers segment by industry, funnel stage, country, language or query intent. Once those dimensions are added, the idea of one universal AI citation strategy becomes even harder to defend.
For GEO teams, the operational shift is straightforward: measure the engines separately, inspect the source classes each one retrieves for your own queries, and avoid turning any third-party monthly leaderboard into a permanent algorithmic truth.
Ahrefs’ September Brand Radar snapshots provide a useful map of the current terrain. What they show most clearly is that there is no single terrain to optimize for.