What changed in the last week
The change was found by users, not announced. A post on Reddit's r/SEO forum reported that links leaving Gemini now carried UTM parameters, the tags marketers append to a web address so analytics software can say where a visit came from. Search Engine Journal picked it up on 1 October. In the thread, John Mueller, who handles search relations for Google, wrote: “Nice. I see it too. Doesn't Gemini have a referrer too though? I thought you could already track them.”
Another user replied that Gemini's referrer mostly survives only on desktop, and put the share that comes through from the Gemini mobile app at about 9 per cent. That figure came from an anonymous account with no method attached, and we do not rely on it. Mueller's answer is the more useful part: he asked for examples he could reproduce, offered to pass them to the team, and said it “would be great to have these retained (in addition to the UTM-tagging)”. In other words, a Google employee confirmed the tags exist and implied that the referrer is not always being passed.
What has not been published is the substance. Google has not said what the parameters contain, whether every outbound link carries them or only some, or whether they appear in the Gemini app, on the web, or both. Search Engine Journal noted that ChatGPT tags only links from answers grounded in a web search, and that nobody yet knows whether Gemini behaves the same way.
Two ways a visit gets its label
Analytics software decides where a visit came from in two main ways. The first is the referrer: when someone clicks a link, the browser normally tells the destination site which page the click came from. The second is a tag written into the link itself, most commonly UTM parameters such as utm_source. The referrer depends on the browser and the app passing it on, and it is often stripped by apps, in-app browsers and privacy settings. A tag travels in the address, survives most of those routes and also appears in a site's raw server logs.
ChatGPT has documented its tag. OpenAI's FAQ for publishers says sites that allow its search crawler can track ChatGPT referrals in tools such as Google Analytics because ChatGPT adds utm_source=chatgpt.com to referral links. That gives a site two ways to see a ChatGPT visit: the referrer, when it survives, and the tag.
Google Analytics 4 handles the referrer side automatically. Its default channel definitions now include an AI Assistant channel: when the referrer matches Google's list of AI assistants, Analytics sets the medium to “ai-assistant” and the campaign to “(ai-assistant)”, and the visit lands in that channel. Search Engine Journal reported the channel's arrival in May. Google's help page names ChatGPT, Gemini, Deepseek, Copilot and Grok as examples, but does not publish the full list.
AI chatbot market share, percent, worldwide, September 2026, StatCounter Global Stats
Source: StatCounter Global Stats, AI Chatbot Market Share Worldwide, September 2026.
StatCounter measures traffic to the more than 1 million sites carrying its tracking code and does not document the chatbot series separately. A count built on referrals misses visits that arrive with no referrer, as described above. Google's AI Overviews and AI Mode are not included.
The two signals can disagree. A link tag that sets a source or medium of its own may decide how a visit is filed, and because Google has not published the values in Gemini's tags, we cannot say whether tagged Gemini visits will land in the AI Assistant channel or somewhere else. The practical check is to look at the source and medium recorded for recent Gemini sessions rather than assume.
The gap: Google's own AI answers
The AI Assistant channel is defined to exclude AI Overviews and AI Mode. A visit from a link in Google's AI answers arrives from google.com like any other search click, and Analytics files it as organic search.
Search Console does not separate those clicks either. Its help page says that clicking a link to an external page in an AI Overview, or in AI Mode, “counts as a click”, under the same rules as other results. Its AI report, released to all sites on 31 August, shows impressions in AI Overviews and AI Mode but no clicks, as set out in what Search Console shows for AI answers. A site can therefore see how often it appeared in Google's AI answers, and how many clicks it got from Web search as a whole, but not how many of those clicks came from the AI answers.
That gap is why the parameter reported on 2 October drew attention. Tom Pool posted screenshots of AI Overview and AI Mode links ending in ?st_source=ai_overview, which would have marked those clicks. Barry Schwartz of Search Engine Roundtable could not reproduce it, and Pool later told him that a Chrome extension had been rewriting the links, “presumably to sell the data on to brokers”. Google had added nothing. Anyone who finds an unfamiliar tag in their analytics should check where it came from before treating it as a new signal.
Not every link in an AI Overview goes to a website. Search Engine Journal described a recording made on 21 September in which underlined text inside an AI Overview opened a conversation in AI Mode instead of a web page. A click like that is not a visit to anyone's site and will not appear in any site's analytics.
What a company can actually measure
Assistant referrals. In Google Analytics 4, the AI Assistant channel is now the first place to look for visits from ChatGPT, Gemini, Copilot and the other assistants on Google's list. It counts only visits whose referrer survived, so it understates the total.
Tagged visits. Searching server logs or analytics for utm_source=chatgpt.com catches ChatGPT visits that lost their referrer. Once Gemini's tag values are known, the same check will work for Gemini. The same visit can carry both a referrer and a tag, so the two counts should not be added together.
Direct traffic. Some AI-referred visits still arrive as “direct”, with neither a referrer nor a tag. There is no way to identify them individually.
Google's AI answers. The only measure is impressions in Search Console's AI report. Set against the Web search click total over the same period, the trend shows whether appearances in AI answers are growing faster than clicks, but it cannot give a click-through rate for AI answers.
For scale, the volumes are small. Cloudflare's crawl-to-referral figures, set out in how much traffic AI assistants actually refer, show assistants reading far more pages than they send visitors to. Better attribution will not change that ratio. It will mainly show which of a company's pages, and which pieces of coverage about it, send AI-referred visitors at all.
Methodology and limitations
This is an explainer built from published documentation and reporting, read on 5 October 2026. ChatGPT's tagging is quoted from OpenAI's “Publishers and Developers FAQ”, which refused our direct requests and was read in full through a text-rendering proxy. The AI Assistant channel is quoted from Google Analytics Help, “[GA4] Default channel group”, and Search Console's click rules from Search Console Help, “Performance report (Search results)”, both read directly. The Gemini tagging and John Mueller's replies are taken from Search Engine Journal's reports of 1 and 3 October. Reddit refused our requests for the original thread or served a login page, so we have read it only as quoted there. The anonymous 9 per cent referrer figure in that thread is reported as a claim and not used as evidence. The st_source episode is from Search Engine Roundtable's report of 2 October and its two updates; the AI Mode link recording is as described by Search Engine Journal on 25 September. We did not test Gemini or ChatGPT ourselves and have no analytics data of our own on AI referrals. We do not know what values Gemini's tags contain or how Google Analytics will file tagged Gemini visits. Google may document, change or remove the tagging at any time.
Conclusion
For the AI assistants, attribution is better than it was a year ago. ChatGPT tags its links, Gemini has started to, and Google Analytics now separates recognised assistants into a channel of their own without any setup. A company can now see, roughly, how many visitors ChatGPT and Gemini send it and which pages they land on, provided it remembers that the channel misses visits that lost their referrer. Google's own AI answers are the blind spot. Google reports how often a site appears in AI Overviews and AI Mode, but it does not separate the clicks, and its analytics channel leaves those answers out by design. Until that changes, the visits Google's AI answers send are counted as search clicks and cannot be told apart.
Frequently Asked Questions
Does Gemini add UTM parameters to its links?
Yes, according to users who spotted them in late September and to Google's John Mueller, who said he could see them too. Google has not documented the tags, so their values and which links carry them are not known.
Does ChatGPT tag the links it sends?
Yes. OpenAI's publisher FAQ says ChatGPT automatically adds utm_source=chatgpt.com to referral links from its search results, so visits can be identified in analytics tools.
Where does AI traffic appear in Google Analytics 4?
In the AI Assistant default channel, when the visit's referrer matches Google's list of AI assistants, which includes ChatGPT, Gemini, Deepseek, Copilot and Grok. Visits whose referrer was stripped can still land in Direct.
Can I see clicks from AI Overviews or AI Mode?
Not separately. Google Analytics files them as organic search and its AI Assistant channel excludes them by definition. Search Console counts them as ordinary clicks and its AI report shows impressions only.
Has Google started tagging AI Overview links?
Not as far as anyone has shown. A parameter reported on 2 October, st_source=ai_overview, turned out to be added by a Chrome extension, according to the person who first reported it.
Will better tracking show more AI traffic?
It will show more of the AI traffic that already exists, mostly visits that previously arrived as direct. It does not change how many visitors AI assistants send, which measurements so far put far below what they read.
Sources
- trade press Roger Montti, Search Engine Journal, Google Gemini Adds UTM Parameters For Referral Attribution, 1 October 2026. Reddit thread and John Mueller's replies, quoted. Secondhand. Read 5 October 2026.
- trade press Matt G. Southern, Search Engine Journal, Google Wants AI Content Fact-Checked, Gemini UTM Tags – SEO Pulse, 3 October 2026. Secondhand. Read 5 October 2026.
- blocked source r/SEO, Google Gemini add UTM to results, late September 2026. Reddit refused our requests or served a login page; read only as quoted by Search Engine Journal.
- official OpenAI, Publishers and Developers FAQ. ChatGPT adds utm_source=chatgpt.com to referral URLs. Read 5 October 2026 through a text-rendering proxy.
- platform documentation Google Analytics Help, [GA4] Default channel group. AI Assistant channel definition and rule; excludes AI Overviews and AI Mode. Read 5 October 2026.
- platform documentation Search Console Help, Performance report (Search results). Click, impression and position rules for AI Overviews and AI Mode. Read 5 October 2026.
- trade press Barry Schwartz, Search Engine Roundtable, Google Tests URL Tracking Parameters To AI Overviews & AI Mode, 2 October 2026, with updates attributing the parameter to a Chrome extension. Read 5 October 2026.
- trade press Matt G. Southern, Search Engine Journal, Google Analytics Adds AI Assistant As Default Channel Group, 14 May 2026. Read 5 October 2026.
- trade press Matt G. Southern, Search Engine Journal, Google AI Overviews Have More Links, But Not All Reach The Web, 25 September 2026. AI Overview link that opens AI Mode. Secondhand. Read 5 October 2026.
- vendor research StatCounter Global Stats, AI Chatbot Market Share Worldwide, September 2026 figures, with its FAQ on methodology. Read October 10, 2026.