Gemini’s brief experiment with UTM tagging on cited links is over. For roughly three weeks in September 2026, Google’s assistant appended utm_source=gemini to outbound URLs, then stopped around September 28-29 without documentation or explanation. The result: a portion of Gemini-driven traffic has slipped back into the murky Direct bucket, and marketers are left to audit the fallout themselves.
A tag appears, then disappears
Natzir Turrado, a search consultant who publishes server-log data, saw tagged visits climb from almost nothing around September 9 to a peak of 83 on September 28. The next day, his logs recorded 3. His chart, which excludes bots, shows the drop landing on the next day. Search Engine Roundtable’s Barry Schwartz reported on October 30 that he could no longer see utm_source=gemini on any Gemini links.
Google has not documented the launch or the removal, and has offered no statement on why it happened or whether the tag will return.
Why that little parameter mattered
UTM parameters identify a source even when the browser sends no referrer. On desktop, Gemini clicks still carry a gemini.google.com referrer, so GA4 can classify them as referrals. The mobile apps are the problem. Turrado says the Gemini iOS app opens links in a WebView and sends no referrer, so GA4 drops those sessions into Direct. Android visits are even harder to separate.
- Desktop web: visible through the Gemini referrer
- iOS app: no referrer, so Direct in GA4; visible in server logs via the GeminiiOS user agent
- Android: falls into Google’s generic agent or Direct, mostly untraceable
For those three weeks, the tag was the one signal that caught some of those app clicks. Turrado estimates the parameter surfaced 16 to 65 extra Gemini visits for every 100 the referrer identified, and puts Gemini’s minimum share of Direct at 0.05% to 0.23% in a normal week.
Direct traffic hides the loss
This is not the first AI attribution gap. In October 2026, ChatGPT temporarily lost its utm_source=chatgpt.com tag after GPT-6 launched. Adobe’s Cedric Huesler measured about 31,000 fewer ChatGPT visits and 26,000 more Direct visits per day. The tags returned and Huesler called it a bug. Gemini’s tag, by contrast, had been missing for a month when Schwartz checked.
Turrado’s longer analysis of AI traffic measurability points to a hidden risk: when AI tags disappear, the misattributed visits land in a bucket whose daily swings are often larger than the lost traffic. Nothing in a standard dashboard flags the change.
What to do before the next tag disappears
Don’t wait for Google to document its tagging status. Build a measurement process that doesn’t depend on a single parameter.
First, audit Direct traffic against a baseline, especially around September 28-29. Second, create a custom AI chatbot channel in GA4 using a referrer regular expression that matches Gemini, ChatGPT and other assistants. Third, check raw server logs for the GeminiiOS user agent when you need to recover iOS app visits.
The timing matters because Alphabet said on October 28 that the Gemini app had passed one billion monthly active users, up from 650 million a year earlier. That is a large audience whose outbound clicks are now harder to count. Publishers weighing AI citations and marketers comparing organic AI visibility against paid channels need a defensible number, not a Direct bucket that quietly absorbs the gap.
Source: PPC Land
