Semrush spent seven months running fixed monthly sets of 2.5 million UK and 25 million US prompts through ChatGPT, Gemini and Google AI Mode, then layered in a larger Google AI Overviews dataset on top. Out of everything AI platforms mentioned across that haul, only 15 domains showed up in the top 100 most-mentioned brands on all four platforms, every single month, in both countries. Amazon, Apple, Google, Microsoft, Reddit and YouTube made the list. Most of the web did not.

The report landed October 13, 2026, and it is the most detailed public look yet at who AI search actually talks about — and, separately, who it actually cites. Those turn out to be two different lists.

📋 How this was put together

The findings below come from Semrush's own 2026 AI Visibility Index release, published October 13, 2026, and the related expanded index report covering the full 126-million-prompt dataset. Independent coverage of the Tesco/Asda citation gap is cited separately from PPC Land. BuzzRiding did not run this study and cannot verify Semrush's raw data; the numbers are reported, not re-tested. Where this piece compares Semrush's findings to BuzzRiding's own AI-citation experiments, those experiments are BuzzRiding's first-hand work, evidenced separately and linked below.

What Semrush actually measured

The index tracks two different things that are easy to conflate: how often a brand gets mentioned in an AI-generated answer, and how often a domain gets cited as a source. Semrush pulled both, across ChatGPT, Gemini, Google AI Mode, plus a larger variable dataset of Google AI Overviews results tied to real search keywords, from January through July 2026.

This edition is the first to add a UK benchmark alongside the existing US data, built from a separate 2.5-million-prompt monthly set engineered to mirror real UK search behaviour. That split is what makes the comparison interesting: it is not one AI platform's quirks, it is four platforms compared against themselves in two different markets.

The universal core: 15 domains, every platform, every month

Semrush calls the stable set "Universal Core" domains — brands that land in the top 100 most-mentioned list on every platform it tracked, every month of the study, with no gaps. The US list ran to 36 domains. The UK list ran to 24. The overlap between the two lists was just 15: Amazon, Apple, Google, Microsoft, Reddit, YouTube and nine others common to both markets.

The UK-only names on that list skew retail. Six of the nine UK-specific Universal Core domains are retail or ecommerce brands, Tesco and Asda among them. That is a narrower, more concentrated picture of "always-visible" than most marketers probably assume going in.

Platform agreement was also weaker in the UK than the US. Any two platforms shared 63 to 70 of their top 100 UK brand mentions in a given month; in the US, that overlap ran 70 to 78. A UK brand's AI visibility depends more on which platform someone happens to be using than a US brand's does.

Mentioned vs. cited: the gap nobody optimizes for

Here is the finding most marketers will not see coming. Fewer than half of the top 100 most-mentioned brands were also among the top 100 most-cited domains. In the UK, that overlap ranged from roughly 37 to 45 domains a month, out of 100.

Semrush's own example makes the gap concrete. In July 2026, Tesco ranked 25th among ChatGPT's most-cited UK domains. Asda — a brand AI platforms mention constantly, per PPC Land's coverage of the same dataset — ranked 606th on citations. Same category, same AI platform, same month. One brand's name coming up in an answer is not the same signal as being the page the answer links back to, and the gap between those two things can run into the hundreds of ranks.

"Tesco ranked 25th in ChatGPT citations in July. Asda, a brand AI platforms mention just as often, ranked 606th. Being talked about and being linked to are not the same metric."

News sites punch above their weight — more in the UK than the US

Source mix varied by platform and country in a way that matters for anyone doing outreach or digital PR. News sites made up 29.5% of ChatGPT's top 100 UK citations, versus 19.6% in the US. On Gemini, news was the single leading UK source category every month in the study, running 16.6% to 23.0%.

Citation concentration told a similar story. In the UK, AI Mode's top ten source domains accounted for 23.2% to 35.8% of all citations in a given month. For ChatGPT, the same top-ten slice was only 12.8% to 15.4%. AI Mode leans on a smaller set of sources much harder than ChatGPT does, at least in the UK market Semrush tested.

Where BuzzRiding's own numbers land next to Semrush's

This site has been running a much smaller version of the same question since September. Each month, BuzzRiding puts eight fixed marketing-related prompts through Google AI Mode, logged out, and records every domain the answers cite. Results live in September's run and October's repeat: 48 cited domains in September, 51 in October, zero mentions of BuzzRiding in either month, and only 20 domains cited in both — roughly 60% turnover in a single month.

Semrush's 126-million-prompt study and BuzzRiding's eight-prompt one are not the same instrument — different scale, different query sets, different time window. But the shape rhymes. Semrush's "Universal Core" is small (15 domains survive across everything, every month) precisely because the rest of the citation landscape churns, platform to platform and month to month. BuzzRiding's own 60% domain turnover between two monthly runs is a small, local echo of the same instability, measured independently and for entirely different queries. Neither number proves the other. Seeing them side by side is still useful: a single good AI Mode citation this month is not a position anyone should assume holds through next month, at either scale.

What this means if you are not Tesco

Most of the coverage of this index is written for enterprise brand teams with the budget to chase a "Universal Core" slot. That is not BuzzRiding's reader. Three things from this data are useful regardless of budget:

  1. Track citations, not just mentions. If you are watching AI search visibility at all, watching only how often your brand name comes up misses the Tesco/Asda gap entirely. The metric that correlates with actual referral traffic is the citation — the link — not the mention.
  2. Earned media and digital PR matter more in AI answers than they do in classic SEO right now, at least in the UK result set, where news sources took nearly 30% of ChatGPT's citation share. A strong relationship with a trade publication or local news outlet may do more for AI visibility than another round of on-page optimization.
  3. Do not treat one good month as a trend. Both Semrush's large-scale data and BuzzRiding's own small-scale experiment point the same direction: the set of cited domains moves between months. A visibility tool's dashboard showing you were cited last month is a snapshot, not a guarantee.

Tools built specifically to track this — rather than a one-off index report — are covered separately in BuzzRiding's own comparison of HubSpot AEO, Otterly.ai, Profound and Mangools and its roundup of GEO tracker tools, for anyone who wants ongoing numbers rather than a single index snapshot.

💡 Key takeaway

Semrush's 2026 AI Visibility Index found that only 15 domains stay in the top 100 AI-mentioned brands across every platform and month it tracked — and that fewer than half of mentioned brands are also cited sources. BuzzRiding's own, much smaller citation experiment shows the same instability at a fraction of the scale: roughly 60% of cited domains changed in a single month. Track citations, not mentions, and do not bank on this month's result repeating next month.

The obvious caveat

This is Semrush's data, reported and linked, not independently re-run by BuzzRiding. Adobe completed its acquisition of Semrush on April 28, 2026, and the October release cites a separate Adobe Analytics stat — AI-referred visitors converting 60% better and generating 53% more revenue per visit than non-AI traffic — without disclosing its own methodology in the same release. That figure is included above for context, not verified here. Semrush's full prompt sets and raw per-domain data are not public, so the brand- and domain-level rankings above should be read as Semrush's own measurement, not an outcome this site confirmed independently.

Frequently Asked Questions

What is Semrush's AI Visibility Index?
A recurring Semrush study tracking which brands AI platforms mention and which domains they cite as sources, across ChatGPT, Gemini, Google AI Mode and Google AI Overviews. The October 2026 edition added a UK benchmark alongside existing US data, covering January to July 2026.
How many domains appear consistently across all AI platforms?
Semrush found just 15 domains — including Amazon, Apple, Google, Microsoft, Reddit and YouTube — appeared in the top 100 most-mentioned brands on all four platforms tracked, every month, in both the UK and US.
Is being mentioned by an AI platform the same as being cited?
No. Semrush found fewer than half of the top 100 most-mentioned brands were also among the top 100 most-cited domains. Tesco ranked 25th in ChatGPT's UK citations in July 2026 while Asda, a frequently mentioned brand, ranked 606th.
Does BuzzRiding have its own AI citation data?
Yes. BuzzRiding runs a monthly experiment putting eight fixed marketing prompts through Google AI Mode and logging every cited domain. Across its first two runs, roughly 60% of cited domains changed month to month, a smaller echo of the churn Semrush's larger study also found.
Who owns Semrush?
Adobe completed its acquisition of Semrush Holdings, Inc. on April 28, 2026. Semrush continues operating as "Semrush, an Adobe Company," with no immediate changes to its services or customer agreements stated at the time.

This post was researched and refined with AI tools.