The short answer. Check GA4’s default channel group first: it now has an AI Assistant channel for visits “from sources like ChatGPT, Gemini, Deepseek, Copilot, or Grok”. It excludes Google’s AI Overviews and AI Mode, which count as Google Search traffic. If you need your own definition, for example to add assistants the built-in list does not name, create a custom channel group with a source regex and place it above Referral. Either way, referral data counts visits that followed a link in an answer. It cannot count mentions, citations nobody clicked, or visits that arrived without a referrer.
What does GA4’s AI Assistant channel count?
Google’s default channel group page lists AI Assistant alongside Organic Search, Referral and the other default channels. It defines it as “the channel by which users arrive at your site from sources like ChatGPT, Gemini, Deepseek, Copilot, or Grok”, and states: “It excludes Google’s AI Overviews and AI Mode.”
The rule is a list match. If the referrer matches GA4’s list of AI assistants, GA4 sets the medium to ai-assistant and the campaign to (ai-assistant), and the session goes into the channel. The page links a downloadable spreadsheet of the sources behind each default channel; check it for the assistants that matter to you. Perplexity and Claude, for example, are not named in the definition itself.
Two consequences:
- AI Overviews and AI Mode clicks are not here. They are Google Search, so they count as Organic Search in GA4. Their impressions are reported in Search Console’s Generative AI performance report.
- The help page does not say whether the channel applies to historical data. Compare periods with care, or use a custom channel group, which Google says can be applied retroactively.
How do you see it?
Open the traffic acquisition report and look at the session default channel group. AI Assistant appears as a row when the property has received matching sessions. Add the landing page as a secondary dimension to see which pages the visits reached, and your key events to see whether they did anything once there.
For ChatGPT specifically there is a second signal. OpenAI’s Publishers and Developers FAQ says “ChatGPT automatically includes the UTM parameter utm_source=chatgpt.com in referral URLs”, so the visit can be attributed to chatgpt.com from the landing URL itself, not only from the referrer.
When do you need a custom channel group?
When you want to choose which assistants count. Google’s custom channel groups page includes an AI-assistants example. The steps, from that page:
- In Admin, under Data display, click Channel groups. You need Editor access or higher on the property.
- Click Create new channel group. It starts as a copy of the default group.
- Add a channel named, for example, “AI assistants”, with a condition on the source that matches regex.
- Reorder the channels so it sits above Referral. Google explains why: “Traffic is included in the first channel whose definition it matches given the current order of channels in the group.”
- Save, then choose the custom group in your acquisition reports.
A standard property can have two custom channel groups in addition to the predefined one. Google says custom groups “can be applied to your reports retroactively”, which makes them the better choice for comparing months. It also says you “should update your regex expression if URLs or the list of assistants you wish to measure change”: products move hosts, as ChatGPT did from chat.openai.com to chatgpt.com.
Our free AI referral segment builder writes the regex from a maintained list of assistant hosts, including Perplexity and Claude, with a copy button. The same expression works as an exploration segment (Google’s segment help) if you only need a one-off analysis rather than a permanent channel.
Answer with a link
An assistant cites the page and the reader clicks.
Referrer or UTM
The visit carries a referrer, or a tag such as utm_source=chatgpt.com.
No referrer and no tag: GA4 has nothing to match
Channel rules, in order
Your custom AI channel, if it sits above Referral, or the default AI Assistant channel.
Report
Sessions, landing pages and key events by channel.
Not in this path
AI Overviews and AI Mode clicks count as Organic Search; mentions without a click are not counted at all.
What does referral traffic not tell you?
Less than it seems to.
- Mentions and unclicked citations. An answer that names you, or cites you without a click, leaves no trace in analytics. Our sampling method measures those directly.
- Which answer sent the visit. The source is the assistant, not the question or the conversation.
- Visits with no referrer. If an app or browser passes neither a referrer nor a tag, GA4 has no source to match, and the session lands in another channel.
- Google’s AI features, as above: they count as Organic Search.
What our case studies show
Four of the sites in our case studies record ChatGPT as a source in their GA4 exports. The figures below are the ones published in each case study, as sessions with source chatgpt.com:
| Site | Sessions from chatgpt.com | All sessions in the export |
|---|---|---|
| woodcharcoal.in | 51 | 446 |
| onlinephotoprinting.co.nz | 23 | 231 |
| firebrickssource.com | 30 | 323 |
| shopifywebdeveloper.co.uk | 16 | 201 |
On woodcharcoal.in, the same export recorded one session from Perplexity against those 51 from ChatGPT. The numbers are small and the sites are young; read them as evidence that the channel exists, not as a forecast. Each case study states its window and its attribution limits.
A checklist
- The traffic acquisition report shows the AI Assistant channel, and you have checked which assistants its source list covers.
- If you need a different definition, a custom channel group has an AI channel above Referral, with a source regex.
- The regex includes old and new hosts, such as
chat.openai.comandchatgpt.com. - Landing pages and key events are reviewed for AI sessions, not just the session count.
- AI Overviews and AI Mode are measured in Search Console, not in this channel.
- Mentions and citations are measured by sampling, because referrals cannot see them.
What we don’t claim
- We do not claim referral traffic measures AI visibility. It measures clicks, which are a small and variable share of the times an answer names or cites a site.
- We do not claim the AI Assistant channel or our regex catches every assistant. Both are lists, and lists go out of date.
- We do not claim the details are permanent. Google’s Analytics help pages change; re-read them before relying on this.