TLDR
Google Gemini has started appending UTM parameters that identify it as the referring source to outbound links in its chat responses, first spotted in the r/SEO community on 30 September 2026. Google's John Mueller said he could see it too, but Google has not documented when the tags are applied. Brands can now capture Gemini referral traffic in Google Analytics 4 (GA4) without extra setup using the built-in AI Assistant channel.
KEY TAKEAWAYS
What was spotted and when
Members of the r/SEO community reported on 30 September 2026 that Google Gemini had started appending UTM parameters to outbound links inside its chat responses, identifying Gemini as the source.[1] The observation spread quickly among practitioners who had been watching AI referral traffic since ChatGPT added its own tags earlier in the year.
John Mueller, Google's Search Advocate, said in the same thread that he could see it too, and asked whether Gemini's referrer was not already enough to track. "If someone has more information on what happens with the referrer (ideally with something I can reproduce), I'm happy to forward that to the team. It would be great to have these retained (in addition to the UTM-tagging)," Mueller said.[1] Google has not published documentation on when the tags are applied, and Mueller's request for reproducible examples suggests the search team is still mapping the behaviour.
Why AI traffic has been invisible
The problem is structural. When a user taps a link inside an in-app browser or an AI assistant interface, the referrer header that identifies the source is frequently stripped before the request hits the destination server. Only about 9% of Gemini mobile-app referrer data passes through at all, and Android Assistant invocations strip the referrer entirely, according to CrawlWarden figures cited by Search Engine Journal.[5] Genuine referral traffic ends up hidden inside a catch-all "direct" bucket, the same problem that plagued early mobile analytics.
ChatGPT already handles its version of this. OpenAI's Publishers and Developers FAQ states: "ChatGPT automatically includes the UTM parameter utm_source=chatgpt.com in referral URLs, enabling clear tracking and analysis of inbound traffic from ChatGPT search results."[2] A UTM tag appended directly to the URL survives the referrer-stripping that happens in-app. Gemini's move follows the same logic.
For Australian brands, Similarweb data, reported by Prompt the Market in September, shows ChatGPT's share of generative AI web traffic fell from 76% to 53% in the year to May 2026 as Gemini's share tripled, making Gemini referral measurement newly material for any brand that had treated AI search as a ChatGPT-only concern.[6] When one platform holds more than half the category and its traffic is invisible in your analytics, the budget decisions that follow are built on bad data.
Measuring it in GA4
Google Analytics 4's (GA4) Default Channel Group already includes a preconfigured AI Assistant channel that automatically captures sessions from ChatGPT, Gemini, Deepseek, Copilot and Grok without any additional setup.[4] Marketers who want finer control can also build custom channel groups in GA4 using regular expressions that match specific AI referrers, including chatgpt.com, gemini.google.com, perplexity.ai and copilot.microsoft.com.[3]
Gemini traffic that previously landed as direct can now be attributed, counted and compared against organic search and paid channels inside the same GA4 report. That makes it possible to build a line in a media plan that says Gemini sends X sessions converting at Y rate, which is the number a budget conversation needs.
Mueller's caveat is worth tracking. Google has not published rules for when the tags are applied, so some Gemini visits will still arrive without a UTM if the tagging is not applied across every surface. Mueller's invitation for reproducible referrer data suggests the behaviour is still being mapped, and the final documentation may narrow or widen the scope of what gets tagged. Practitioners can run their own GA4 comparison between the AI Assistant channel and direct traffic from Gemini domains over the first two weeks of October 2026 to gauge coverage.
SOURCES & CITATIONS
- Google Gemini adds UTM to results, r/SEO Reddit thread including John Mueller comment
- OpenAI Publishers and Developers FAQ
- GA4 Help Center, Custom channel groups
- GA4 Help Center, Default channel group including AI Assistant
- Search Engine Journal, Google Gemini adds UTM parameters for referral attribution
- Prompt the Market, ChatGPT AI search share drops from 76% to 53% as Gemini surges
FREQUENTLY ASKED QUESTIONS
What UTM parameters does Google Gemini append to outbound links?
How do I see Gemini traffic in Google Analytics 4?
Why has AI referral traffic shown up as direct in analytics until now?
Did ChatGPT do this before Gemini?
James Dore is founder and editor of Prompt the Market and Strategy Director at Bushnote, a Sydney strategy, SEO and AI search agency. He has a background in strategy, media and financial services, and led consumer product marketing at MONEYME. He writes on AI search, answer engines, technology policy and media economics.
