More people ask ChatGPT, Gemini or Perplexity before searching Google, and those assistants cite sites with links. GA4 has no default “AI” channel: it lumps those visits into referral or direct. Here is how to set up the measurement in an afternoon and read it without over- or underestimating.

Step 1: look at what is already there

In Reports → Acquisition → Traffic acquisition, set the primary dimension to Session source and look for chatgpt.com, gemini.google.com, perplexity.ai, copilot.microsoft.com, claude.ai.

Step 2: an “AI” channel in your channel group

  1. Admin → Data display → Channel groups, copy the default group.

  2. Add an “AI” channel with Source matches regex:

    chatgpt\.com|openai\.com|gemini\.google\.com|bard\.google\.com|perplexity\.ai|copilot\.microsoft\.com|claude\.ai|deepseek\.com|meta\.ai

  3. Place it above Referral. GA4 assigns each session to the first matching channel.

Custom channel groups apply retroactively, so you see the trend right away. Review the domain list from time to time.

Step 3: understand what gets lost

The number is a floor:

  • Apps and in-app browsers often send no referrer, so GA4 counts the visit as direct.
  • UTMs can disappear. ChatGPT adds utm_source=chatgpt.com to many links, but it is not guaranteed. In 2026, Gemini links were reported to stop carrying utm_source=gemini around late September, without official confirmation. Annotate that period before concluding you lost visits.
  • People read the answer and then search your brand, which shows up as branded search.

If the channel matters, add “ChatGPT or another AI” to a “how did you hear about us?” question, the same logic as tracking WhatsApp clicks.

Step 4: separate people from agents

Agents that browse on a user’s behalf can execute GA4 and register as sessions. In October 2026 Microsoft Clarity published an analysis of over five million agent sessions and opened its Agent Activity Dashboard to projects with detected agent traffic, a free way to check. In GA4, investigate spikes with zero engagement, data-center cities, odd screen resolutions, and conversions sales does not recognize. Test the signals on a sample before excluding traffic; if those conversions feed bidding, agent form fills pollute the signal like bots do. See impressions but no conversions.

What to do with the data

Check which pages get AI traffic (usually pages answering a specific question), compare conversion rate and engagement against organic, and use the GA4 BigQuery export for session-level detail.

I followed the Gemini signal and the Clarity study in Yoann Ferrand’s Paid Media News newsletter.