How to track AI assistant traffic in GA4

If you are pulling October numbers for a month-end report, AI assistant traffic is the line most likely to mislead you. GA4 now gives chatbot visits their own channel, but ChatGPT stopped tagging its links for about a week in October and Gemini stopped adding its UTM tag around September 28, so a drop on the chart may be a tracking change.

The short answer: use GA4’s built-in AI Assistant channel for recent months, add a custom channel group so you can see the same traffic before the channel existed, mark October 8 to 15 and September 28 with annotations, and read Direct next to AI before you report a decline.

Does GA4 track AI assistant traffic on its own now?

Yes. Since May 13, 2026, GA4’s default channel group has an AI Assistant channel, and you don’t need to set anything up. Google’s “What’s new” entry says it covers chatbots like ChatGPT, Gemini and Claude. When a visit’s referrer matches Google’s list of AI assistants, GA4 sets the medium to ai-assistant and files the session under AI Assistant instead of Referral. It shows up as a row in the Traffic acquisition report (Reports, then Acquisition).

What does the AI Assistant channel miss?

It misses anything before it existed, anything Google doesn’t recognise, and Google’s own AI features:

• History. The channel works going forward. Older sessions keep their Referral label, so a year-on-year chart shows AI traffic appearing from nowhere in May.
• The full list. Google names examples (ChatGPT, Gemini, DeepSeek, Copilot, Grok) but doesn’t publish the full list of assistants it recognises.
• AI Overviews and AI Mode. Google’s channel documentation leaves these out of AI Assistant. Clicks from them count as Organic Search.
• Visits with no referrer. If someone copies a link out of a chatbot app, or the link opens without a referrer and without a tag, GA4 has nothing to go on and calls it Direct.

Also check old segments: a filter built on medium = referral to catch ChatGPT now quietly loses those visits.

How do I see AI traffic from before May 2026?

Build a custom channel group with an AI channel of your own. Google’s help page says custom channel groups apply to your reports retroactively, so one rule covers last year and this month. You need the Editor role, and standard properties get two custom groups.

1. Go to Admin, then under Data display click Channel groups.
2. Click Create new channel group and name it something like “Channels with AI”. It starts as a copy of the default group.
3. Click Add new channel, name it “AI assistants”, click Add condition group, choose Source, choose matches regex and paste the pattern below. Click Save channel.
4. Click Reorder, drag “AI assistants” above Referral (Google’s help page suggests above Organic Search too), then click Apply and Save group. Traffic goes to the first channel it matches, so below Referral it stays empty.
5. Open Traffic acquisition, switch the primary dimension to your new group, and set the date range to before May 13. An “AI assistants” row now appears in months where the default group shows none.

Here is a pattern that covers the common assistants. GA4 regular expressions must match the whole value, which is why it starts and ends with .*:

.*(chatgpt|openai|perplexity|gemini|copilot|claude|deepseek|grok|meta\.ai).*

It catches chatgpt.com, perplexity.ai, gemini.google.com, plain gemini, copilot.microsoft.com, claude.ai and the rest, and it leaves google, bing and facebook.com alone. Google’s help page has a longer example. Whichever you use, read it against your real source list once, because a loose pattern can swallow sources you didn’t mean to include.

Why did ChatGPT traffic drop in October?

Mostly because ChatGPT stopped labelling its clicks, not because people stopped clicking. ChatGPT has added utm_source=chatgpt.com to the links it shows since mid-2025 and most clicks arrive without a referrer, so the tag is what identifies them. Around October 8, the tag disappeared from many links. An analyst who tracks ChatGPT clicks across thousands of sites said OpenAI told him it was a bug, and a fix began rolling out on October 15. OpenAI has not said anything publicly.

Visits from that week with neither a tag nor a referrer were counted as Direct, and they stay Direct. Nobody has mentioned a backfill, so October’s ChatGPT number is an undercount you can estimate but not recover.

Why did Gemini traffic look lower from the end of September?

Because Gemini stopped adding its UTM tag around September 28. In early September it started putting utm_source=gemini on the links it cites, and those tagged visits grew for about three weeks, then vanished overnight. Natzir, an SEO who shared the chart, spotted it, another observer saw the same drop on the same date, and Search Engine Roundtable reported it. Google has not confirmed or explained the change.

Desktop Gemini still sends the gemini.google.com referrer, and those visits stayed flat the whole time. So a report that filters on the source gemini alone shows a fall that did not happen. The pattern above matches both values, so report Gemini as one line.

How do I check whether AI visits ended up in Direct?

Compare AI and Direct traffic on the same pages, day by day, across the gap. Visits that lost their label land on the same pages, so the two lines move in opposite directions.

1. Open Traffic acquisition, filter to your AI channel, and set the date range to September. Add Landing page + query string as a secondary dimension and note the top ten pages.
2. Change the date range to October 1 to 22, show the chart by day, and compare AI and Direct sessions for those pages and for your homepage.
3. Look for Direct rising on the days AI falls, from around October 8 to October 15. That shape means tracking. If Direct stays flat while AI falls, something else changed.
4. Filter Traffic acquisition to session source containing “chatgpt” for a recent week and check which default channel those sessions sit in. If some are outside AI Assistant, report from your custom group.

Some AI visits are never labelled at all. According to the same observer, the Gemini iOS app opens links in its own in-app browser and sends no referrer, so those visits land in Direct every month, not only in October. The only trace is the GeminiiOS user agent in your server logs. GA4 can’t separate them, so mention them as a known gap rather than trying to correct for them.

What should go in the month-end report?

AI traffic with its caveats attached, so nobody acts on a tracking change:

1. Add two annotations. Open any report, click the note icon at the top right, and create one for October 8 to 15 (“ChatGPT links lost UTM tags; visits counted as Direct”) and one for September 28 (“Gemini stopped adding utm_source=gemini to links”). Annotations take a date range; creating one needs the Editor role.
2. Report AI traffic from your custom channel group, so this month compares with last year on the same rule.
3. Show sessions and key events for the AI channel next to Organic Search. When AI visit counts are small, the conversion rate tells you more than the count.
4. List the top landing pages from AI. They show what assistants link to, which guides content work better than the total.
5. Write one line saying what GA4 can’t see: AI Overviews and AI Mode sit inside Organic Search, Gemini app visits sit in Direct, and mentions without a click aren’t counted anywhere in GA4.

Clicks are only half the picture. For whether AI crawlers can read your pages at all, see how to check what AI crawlers see on your WordPress pages and what AI search taught me about SEO, AEO, GEO and CRO.

Set the channel group up today and it is ready for every report after this one. Add the two annotations while October is fresh: by next spring nobody will remember why the line dipped.