How to Track AI Referral Traffic in GA4

AI referral traffic is the set of visits that reach your site from links in AI assistants such as ChatGPT, Perplexity, Gemini, Claude and Copilot. GA4 now groups much of it into a built-in AI Assistant channel, and a custom channel group with a referrer regex lets you control exactly which sources count. Two gaps remain: clicks with no referrer land in Direct, and clicks from Google AI Overviews and AI Mode are counted as Organic Search.

This guide shows where AI referral traffic appears in GA4 by default, how to build a custom channel group with a working regex, and how to estimate what GA4 cannot see.

What counts as AI referral traffic

A visit counts as AI referral traffic when someone clicks a link inside an AI-generated answer and lands on your site. In GA4 that visit is identified by its source, which comes from the referrer header the browser sends or from a utm_source parameter on the link. ChatGPT, for example, appends utm_source=chatgpt.com to the links it shows, according to OpenAI’s publisher FAQ.

It helps to separate three groups, because GA4 treats them differently:

• Standalone assistants such as ChatGPT, Perplexity, Gemini, Claude, Copilot, DeepSeek, Grok and Mistral. These send a referrer most of the time and can be classified.
• Google’s AI surfaces, AI Overviews and AI Mode. They live on google.com, so their clicks look like any other Google organic click.
• Visits with no referrer from apps, AI browsers, links that strip the referrer and copied URLs. GA4 has no way to tell these apart from other Direct traffic.

Referral traffic is only one part of the picture. Many AI answers mention a brand without linking to it, which is why traffic data belongs next to the visibility metrics covered in what AI visibility is and how to measure it.

GA4’s built-in AI Assistant channel

Since May 2026, GA4’s Default Channel Group has included an AI Assistant channel. Google’s traffic-source dimensions documentation defines it as sessions whose medium exactly matches ai-assistant. When the referrer is on Google’s list of AI assistants, GA4 sets the medium to ai-assistant and the campaign to (ai-assistant) automatically. The examples Google gives include ChatGPT, Gemini, DeepSeek, Copilot and Grok.

You will find it under Reports, then Acquisition, then Traffic acquisition, with the primary dimension set to Session default channel group. No setup is needed.

The built-in channel has three limits worth knowing before you rely on it:

• Google has not published the full list of recognized assistants, so you cannot confirm whether a smaller or newer assistant is included.
• It excludes AI Overviews and AI Mode. Google states that those visits remain in Organic Search.
• It depends on the referrer. Assistant clicks that arrive without one still fall into Direct.

For most sites, the native channel is the right starting point. Build a custom channel group when you need to control the source list, report on assistants Google may not recognize, or keep consistent history with a setup you created before May 2026.

How to track AI traffic in GA4 with a custom channel group

A custom channel group reclassifies sessions using rules you write. Google’s custom channel groups documentation confirms three details that matter here: a standard property can have two custom groups in addition to the default, custom groups apply to your reports retroactively, and traffic goes into the first channel whose rule it matches, checked from top to bottom. You need Editor access or higher.

1. Open channel groups. Go to Admin, then under Data display click Channel groups.
2. Create the group. Click Create new channel group. GA4 starts from a copy of the default group, which keeps every standard channel. Name it something like “Channels with AI”.
3. Add a new channel. Click Add new channel and name it “AI Assistants (custom)”.
4. Set the condition. Choose Source as the dimension, matches regex as the operator, and paste the regex below as the value.
5. Save the channel, then reorder. Click Reorder and move your new channel above Referral and above the built-in AI Assistant channel. If it sits below Referral, Referral will claim the sessions first.
6. Save the group. Click Apply, then Save group.
7. Use it in reports. In Traffic acquisition, change the primary dimension to your new group. It also works as a secondary dimension and in explorations.

The referrer regex

This pattern covers the main assistant domains, including the legacy ChatGPT and Bard hostnames and Mistral’s chat domain. It is based on the list published by Terminus, with Mistral added.

^(chatgpt\.com|chat\.openai\.com|perplexity\.ai|www\.perplexity\.ai|gemini\.google\.com|bard\.google\.com|claude\.ai|copilot\.microsoft\.com|chat\.deepseek\.com|grok\.com|chat\.mistral\.ai|meta\.ai|you\.com|poe\.com)$

Three notes on using it. The ^ and $ anchors require an exact match on the whole source value, which prevents false positives such as a domain that merely contains “you.com”. GA4 channel rules are not case-sensitive, so you do not need to handle capital letters. And because the pattern matches exact hostnames, check your own Session source values first and add any variants you actually see, such as a www. or regional subdomain.

Test the regex before you trust it

Open an exploration, add Session source as a dimension and Sessions as a metric, and filter Session source with matches regex using the same pattern. Then run a second filter with a loose pattern such as gpt|openai|perplexity|gemini|claude|copilot|deepseek|grok|mistral. Any source that appears in the loose result but not the strict one is a variant you should add.

Which setup to use

The three options overlap, so pick based on what you need to report.

A sensible default is the built-in channel for monthly reporting, plus an exploration for deeper analysis. Spend a custom group slot only if your team needs a fixed definition that does not depend on Google’s unpublished list.

The no-referrer limitation and why AI traffic hides in Direct

Every GA4 method above depends on a referrer or a UTM parameter. When both are missing, the visit is Direct. That happens with links opened with noreferrer, with in-app browsers and desktop apps, with AI browsers, and when someone copies a URL from an answer and pastes it into a new tab.

The share of AI visits lost this way is not well established. Vendor samples disagree widely, and neither has been independently confirmed. What is documented is how quickly it can change. From about 8 October 2026, ChatGPT links began opening without a referrer and without utm_source, and Search Engine Roundtable reported that ChatGPT visits dropped while Direct rose by a similar amount on the affected sites. UTM tagging was reported restored from 15 October 2026. A similar Google AI Mode bug in May 2025 was fixed within days.

You cannot recover those visits in GA4, but you can spot the pattern:

• Watch Direct sessions that land on deep pages, such as specific guides or comparison pages. People rarely type those URLs, so a sudden rise there often signals lost referrers.
• Compare the AI Assistant channel and Direct week over week. If one falls as the other rises with no campaign change, suspect a tagging change on the assistant’s side.
• Annotate known incidents in your reports so a referrer outage is not read as a loss of AI visibility.

How to track traffic from AI Overviews and AI Mode

Clicks from Google AI Overviews and AI Mode carry a google.com referrer, so GA4 classifies them as Organic Search and no regex can separate them. Google confirms this in the same channel definition that introduced the AI Assistant channel.

Search Console is the closer source. AI Overviews and AI Mode traffic is included in the Performance report under the Web search type, mixed in with classic results. Since June 2026, Google’s generative AI performance reports show impressions by page, country and device for those surfaces, but no clicks, and their figures are a subset of the Web totals.

A workable approach is to track AI Overview presence for your keywords separately, then read Organic Search landing-page data in GA4 alongside it. If a page starts being cited in overviews for its main queries and its organic engagement changes at the same time, the two series together tell the story. The guide on how to appear in Google AI Overviews covers what drives those citations.

Reading AI referral traffic once it is tracked

Raw session counts from AI assistants are usually small, so look at quality and destination rather than volume alone.

• Landing pages. Add Landing page as a secondary dimension. The pages assistants link to show which of your content they treat as a source, which can differ sharply from your top organic pages.
• Engagement and key events. Compare engagement rate and key event rate for the AI channel with Organic Search. Treat small samples with caution.
• Per assistant. Break the channel down by Session source. A rise in one assistant alone usually reflects a change in that engine’s answers, not in your site.

Traffic only shows the visits that happened. To see the prompts where you were mentioned but not clicked, or where a competitor was recommended instead, pair GA4 with prompt-level tracking. Asheard records mentions, citations and position across ten AI engines and offers a free GA4 AI-traffic regex you can copy into the setup above, so referral data and the AI visibility metrics that matter sit in the same report.

Frequently asked questions

Does GA4 track ChatGPT traffic automatically?

Mostly, yes. Since May 2026, GA4 assigns visits from recognized AI assistants, including ChatGPT, to the built-in AI Assistant channel, with the medium set to ai-assistant. ChatGPT clicks that arrive without a referrer or a utm_source parameter are still counted as Direct, so the channel undercounts real ChatGPT traffic during periods when links are opened without a referrer.

Why is ChatGPT traffic showing as Direct in GA4?

Because the visit arrived without a referrer and without a UTM parameter. That happens when a link opens with noreferrer, in an app or AI browser, or when a user copies the URL. In October 2026, ChatGPT links briefly lost both the referrer and the utm_source tag, which pushed many of its visits into Direct until tagging was restored.

Can I see AI Overviews traffic in GA4?

Not separately. Clicks from Google AI Overviews and AI Mode carry a Google referrer, so GA4 counts them as Organic Search, and Google’s AI Assistant channel explicitly excludes them. Use Search Console instead: its Performance report includes AI Overviews traffic under the Web search type, and its generative AI reports show impressions, though not clicks.

Is a custom channel group retroactive in GA4?

Yes. Google’s documentation states that custom channel groups can be applied to your reports retroactively, so a group you create today will classify past sessions too, within your data retention. The exception is audiences: changes to a channel group used in an audience apply only from that point forward. Standard properties can create two custom channel groups.