TL;DR: Google’s Gemini quietly stopped attaching utm_source=gemini to the outbound links it cites, after tagging them for roughly three weeks starting in early September. The change went unannounced, and because Gemini’s iOS app passes no referrer at all, traffic from it now lands in GA4 as plain Direct traffic instead of anything attributable to Gemini.
If your GA4 Direct traffic has looked a little heavier than usual lately, and you cannot explain why, this might be the answer. Sometime around September 28, Google’s Gemini stopped adding utm_source=gemini to the links it cites in its answers, and nobody at Google said a word about it.
The change was caught by SEO Natzir, who goes by @natzir9 on X, after noticing the parameter had simply vanished from Gemini’s citation links. He charted the pattern and found something specific: the tagging rose steadily for about three weeks after it was first introduced in early September, then dropped off overnight once it stopped.
“The cited URLs stopped carrying utm_source,” Natzir noted, adding that on the iOS app specifically, Gemini passes no referrer information at all.
That last detail is the part that actually matters for anyone trying to measure Gemini’s real impact on their site. On the web, Gemini still sends a referrer when someone clicks through from a cited link, so at minimum you can tell the traffic came from somewhere outside your own domain. The iOS app sends nothing. A visit that genuinely originated from a Gemini citation, read on an iPhone, now looks identical in your analytics to someone who typed your URL in directly or opened a bookmark. There is no tag, no referrer, no trail.
Search Engine Roundtable’s Barry Schwartz, who wrote up Natzir’s finding, said he can no longer find the parameter on any Gemini links either, confirming this is not a partial rollback limited to one surface. The article also notes that Google’s John Mueller reportedly saw the utm_source tag on Gemini links in a Reddit comment roughly a month before it disappeared, suggesting the tagging was deliberate and in place for a real stretch of time before someone, for reasons Google has not explained, turned it off.
No official statement from Google accompanies any of this. That silence is consistent with how Google tends to handle changes to AI citation plumbing generally: quietly, without a blog post, and often only confirmed after someone outside the company notices the pattern first. It’s the same posture the company has taken with several other recent tweaks to how AI Mode and AI Overviews link out to publishers, changes that get discovered by SEOs poking at server logs rather than announced on Google’s own channels.
For publishers and marketers, the practical fallout is straightforward even if the cause is murky. Any report built around utm_source=gemini as a way to isolate Gemini-driven traffic from everything else is now stale for anything after late September, and worse, there is no clean substitute. Referrer-based segmentation still works on the web, in a limited sense, but the iOS gap means a real and possibly significant slice of Gemini traffic is now invisible, folded into Direct where it cannot be separated back out.
This lands in the middle of a broader expansion of AI inside Google’s own products. Google is simultaneously rolling ads in AI Mode out to ten more countries and launching multiturn ad formats in the US, all while the attribution tools meant to measure how any of this traffic actually behaves keep quietly shifting under everyone’s feet. Marketers are being asked to optimize for AI visibility in products whose own measurement plumbing changes without notice.
The bottom line
Whatever the reason Google pulled utm_source=gemini, the effect is the same for anyone trying to measure AI-driven traffic: your numbers for the last month are probably undercounting Gemini, and you will not know by how much. Treat any Gemini attribution you are currently reporting with real skepticism until Google says something, which it may never do.
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