How to track AI referral traffic from ChatGPT, Perplexity, Gemini and Copilot in GA4

AI referral traffic is still small for most sites, typically around one percent of sessions in 2026, and it is growing several-fold year on year. It also converts far better than a Google click in most analyses we have seen, because the visitor arrives having already been told you are the answer. If you cannot see it in GA4, you cannot make the case for investing in it. Most businesses cannot: one 2025 study found the large majority of brands could not attribute AI traffic at all.

This is the setup that fixes that in under an hour.

Step 1: Check the native AI Assistant channel

Google added an "AI Assistant" default channel to GA4 on 13 May 2026, rolling out to most properties by June. When GA4 recognises a referrer from ChatGPT, Gemini, Copilot, DeepSeek or Grok, it sets the medium to ai-assistant and files the session under that channel. Open Reports, then Acquisition, then Traffic acquisition, and look for it.

Know its limits before relying on it. It does not include Perplexity. It excludes Google's own AI Overviews and AI Mode, which continue to report as Organic Search with no separate flag. It is not retroactive. And default channel groups cannot be edited, so you cannot add sources to it.

Step 2: Create a custom channel group with an AI Search channel

Go to Admin, then Data display, then Channel groups. Copy the Default Channel Group and name the copy "Channels with AI". Inside it, add a new channel called "AI Search" with the condition Session source matches regex (case-insensitive):

chatgpt\.com|chat\.openai\.com|openai\.com|perplexity\.ai|claude\.ai|gemini\.google\.com|copilot\.microsoft\.com|copilot\.com|you\.com|search\.brave\.com|duckduckgo\.com/aichat

GA4 derives Session source from utm_source when present and from the referrer when not, so this also catches ChatGPT links that carry utm_source=chatgpt.com (ChatGPT began adding that parameter in mid-2025).

Step 3: Reorder the channel above Referral

This is the step people miss. GA4 evaluates channel rules top to bottom, so if Referral is evaluated first, every AI session matches Referral and never reaches your new channel. Use Reorder to drag "AI Search" above Referral (and above Organic Search, to be safe), then Save. Custom channel groups apply at query time, so historical sessions are reclassified too.

Step 4: Build the two reports that matter

Create an Exploration with these dimensions and metrics:

1. Landing page by AI source: dimension Landing page + query string, secondary dimension Session source, filtered to the regex above; metrics Sessions, Engaged sessions, Key events. This tells you which pages AI engines are actually sending people to, which is the closest thing you have to a citation report from inside your own data.
2. Conversion by channel: dimension Session default channel group (choose your custom group), metrics Sessions, Key events, Session key event rate. Compare AI Search with Organic Search and Paid.

Save both to the Library so the team can find them.

Step 5: Capture the AI source on your lead forms

GA4 counts sessions; your CRM counts customers. Add a hidden field to your enquiry forms that captures the referrer or utm_source on page load and passes it into the lead record. Map it to a "First touch source" field in the CRM that cannot be overwritten later. This is how AI traffic becomes pipeline in a board report rather than a line in an analytics dashboard.

Step 6: Accept and document the undercount

Sessions that arrive with no referrer header land in Direct. That includes most traffic from the ChatGPT mobile apps and any link copied out of an answer. 2026 estimates of the referrer-less share range widely, from around a third to two thirds of AI sessions. Two mitigations: watch for unexplained rises in Direct traffic to pages you know AI engines cite, and use the prompt-tracking method in our AI visibility guide to measure mentions that never become clicks at all.

Step 7: Review monthly and extend the regex

Every quarter, open Traffic acquisition filtered to the Referral channel and scan for new AI hostnames. When one appears, append it to the regex. Assistants launch and rename often.

How to know it worked

Traffic acquisition shows an "AI Search" row with sessions in it. The landing-page exploration lists the pages AI engines send visitors to. Your CRM shows leads with an AI first-touch source. You can state, with a number, what AI search is worth to the business this month.

Common mistakes

• Creating the channel and leaving it below Referral. It will show zero forever.
• Trusting the native channel alone and concluding Perplexity sends nothing.
• Treating the measured number as the whole picture rather than a floor.
• Not connecting it to leads, so the finance conversation never happens.