TL;DR

  • GA4's default channel group has no AI channel. Visits from ChatGPT, Perplexity, Gemini and Copilot land in Referral, mixed in with every other site that links to you.
  • A custom channel group fixes that, and it applies to your past data too, not just new sessions.
  • ChatGPT tags its links with utm_source=chatgpt.com, so it's the easiest platform to track. Others rely on the referrer, which is less reliable.
  • Clicks from Google's AI Overviews and AI Mode can't be separated out. They count as ordinary Google search traffic.

Why AI visits disappear in GA4

GA4 sorts every session into a channel using rules it decides for you: Organic Search, Paid Search, Organic Social, Referral and so on. None of those rules know what an AI assistant is. So when someone clicks a citation in ChatGPT or Perplexity, the visit is filed as a referral from chatgpt.com or perplexity.ai, next to a partner's blog and a directory listing.

The traffic is there. It just isn't visible as a channel, so it never shows up in the acquisition report your team actually reads, and nobody can tell whether it's growing.

What each platform sends you

ChatGPT is the most cooperative. OpenAI's publisher FAQ says ChatGPT automatically adds utm_source=chatgpt.com to referral URLs, so those visits arrive with a source GA4 can read even if the referrer is stripped. The same FAQ notes this applies to sites that allow OAI-SearchBot, OpenAI's search crawler, so blocking that bot in robots.txt cuts off more than you might think.

Perplexity, Gemini, Copilot and Claude don't document anything equivalent. When their links pass a referrer, GA4 records the hostname: perplexity.ai, gemini.google.com, copilot.microsoft.com, claude.ai. When they don't, which can happen with app clicks in particular, the visit shows up as Direct and there's no way to recover it.

Set up an AI channel group

You need Editor access or above on the GA4 property. Per Google's channel group documentation, a standard property can have two custom channel groups on top of the default one, so this uses one of your two slots.

Step 1. Go to Admin, then Data display, then Channel groups, and choose Create new channel group. GA4 starts you with a copy of the default group, so all your existing channels carry over.

Step 2. Click Add new channel and name it AI Search. Set the condition to Session source, partially matches regex, and paste this pattern: chatgpt\.com|chat\.openai\.com|perplexity|gemini\.google\.com|copilot\.microsoft\.com|claude\.ai

Step 3. Drag the new channel above Referral. GA4 checks channels from top to bottom and stops at the first match, so if Referral sits higher, it claims these visits first and your new channel stays empty.

Step 4. Save, then open Reports, Acquisition, Traffic acquisition and switch the primary dimension to your new channel group. Because custom channel groups apply retroactively, you'll see AI Search sessions going back over your existing data straight away.

Check the pattern every few months. New assistants appear and domains change, and anything the regex doesn't name falls back into Referral.

What this won't catch

Google's AI features are the big gap. Google treats AI Overviews and AI Mode as part of Search, and clicks from them are counted with the rest of your Google organic traffic in both GA4 and Search Console. There's no filter that isolates them, so any tool claiming to show you exact AI Overview clicks is estimating.

The second gap is the Direct traffic mentioned above. If Direct rises at the same time your brand starts appearing in AI answers, some of that is probably AI traffic arriving without a referrer, but you can't prove which part.

Treat the AI Search channel as a floor, not a total. It's the share of AI-driven visits you can see, and it will undercount.

What to report

Sessions on their own say very little. The more useful view is AI Search sessions next to key events, so you can see whether these visitors sign up, book or buy at a different rate from organic search visitors. We looked at how that conversion picture has shifted in why AI-referred traffic went from converting worst to best.

Then look at landing pages. The pages AI tools send people to show you which content they're citing, which is the closest thing GA4 offers to a citation report. If those pages aren't the ones you'd choose, that's the brief for your next round of GEO work.

Pair the traffic numbers with a manual check of the questions your buyers ask, as we described in what generative engine optimization is. GA4 tells you what AI sent you. It can't tell you how often you were named and not clicked.