Track AI Assistant Traffic in GA4 with UTM Tags

Google Analytics 4 (GA4) has a default channel for visits from AI assistants such as ChatGPT and Gemini. GA4 fills this channel from the referrer of the visit, not from tags that you add. Clicks from Google’s own AI Overviews and AI Mode count as Organic Search instead. You cannot tag the links that an assistant writes. You can tag the links that you place where AI tools read them, such as an llms.txt file.

UTM basics

UTM parameters are tags at the end of a URL that tell analytics where a visit came from, for example ?utm_source=newsletter&utm_medium=email&utm_campaign=spring_sale. UTM stands for Urchin Tracking Module, after the analytics company that Google bought in 2005. GA4 reads utm_source, utm_medium, utm_campaign and some optional parameters, and the values are case sensitive. Google’s Campaign URL Builder makes tagged URLs for you. The UTM tagging guide covers every parameter, the naming rules, encoding and redirects.

The AI Assistant channel in GA4

Google’s default channel group page defines the AI Assistant channel:

• It covers visits from sources like ChatGPT, Gemini, DeepSeek, Copilot or Grok.
• Its rule is that the medium exactly matches ai-assistant.
• If the referrer matches Google’s list of AI assistants, GA4 sets the medium to ai-assistant and the campaign to (ai-assistant).

The page does not publish the full list of assistant referrers. Search Engine Journal reported the new channel on May 14, 2026, and said that it needs no setup. Before the channel existed, the usual method was a custom channel group with a regular expression for AI referrers. Search Engine Journal says that a custom group can still cover assistants that the default list misses.

Find AI visits in your reports

1. In GA4, open Reports, then Acquisition, then Traffic acquisition.
2. Set the primary dimension to Session default channel group, and select the AI Assistant row.
3. To see which assistant sent the visit, add Session source as a secondary dimension.

The dimensions “Landing page + query string” and “Page path + query string” do not show UTM parameters. GA4 keeps the full URL with the tags in the Page location dimension. If a link has both Google Ads auto-tagging and UTM tags, GA4 uses the auto-tagged values for source and medium, as the traffic-source help page explains.

AI Overviews and AI Mode count as Organic Search

The same channel page lists Google’s AI Overviews and AI Mode under Organic Search, not under AI Assistant. A click from an AI Overview therefore appears in the Organic Search channel, mixed with clicks from normal results. Google Search Console does the same. Its AI features page says that sites in AI features are included in the overall search traffic, in the Performance report under the “Web” search type.

Neither tool separates AI Overview clicks from other Google clicks. The Gemini app is a different product. Google names Gemini as an example source for the AI Assistant channel.

Why you cannot depend on utm_source=chatgpt.com

Links in ChatGPT answers have often carried utm_source=chatgpt.com. Do not build your reports on this tag:

• OpenAI’s current help pages do not document the tag (October 2026). OpenAI can change it or drop it at any time.
• Not every cited link carries it. LLM Pulse, a company that sells AI visibility tracking, publishes a daily tagging rate for ChatGPT answers with cited links. It warns that a drop in this rate means that ChatGPT visits are counted as direct or unattributed traffic.
• The tag gives a source but no medium. Google’s URL builder help page says that missing UTM parameters show as (not set) in reports. So a visit can show as chatgpt.com / (not set). Look at Session source / medium in your property to see which channel these visits get.
• Some apps and in-app browsers send no referrer. Without a referrer and without tags, GA4 cannot see where the visit came from, and the visit can land in the Direct channel.

Count AI visits by channel and by session source, and treat the tag as one extra signal. The ChatGPT search guide explains how ChatGPT links to its sources.

Tag your own links in AI-facing places

You do not write the links in AI answers. You do write some files and responses that AI tools read, and you can tag the links in them:

• An llms.txt file, a proposed Markdown file at the root of a site that lists its key pages for language models. No major AI company says that its crawler reads the file, but users can paste it into a chat.
• Links that your own API or MCP server returns to AI agents. MCP (Model Context Protocol) is a standard way for AI apps to call outside tools.

Use one fixed set of values for these links. In this llms.txt example, the source names the file and the medium is ai-assistant:

# Example Docs

> Guides and API reference for Example.

## Docs

- [Quick start](https://www.example.com/docs/start/?utm_source=llms_txt&utm_medium=ai-assistant&utm_campaign=ai_files): Install and first request
- [API reference](https://www.example.com/docs/api/?utm_source=llms_txt&utm_medium=ai-assistant&utm_campaign=ai_files): All endpoints

The rule for the AI Assistant channel matches the medium ai-assistant, so GA4 can group these visits in that channel. Type the medium exactly, with the hyphen. The source llms_txt keeps these visits apart from visits that GA4 found by referrer.

Know the limits before you rely on these numbers:

• No AI vendor documents that it keeps the query string when it repeats a link. Treat tagged visits as a minimum count.
• A tagged URL is a second URL for the same page. Make sure that each page has a canonical link to its clean URL, and list only clean URLs in your sitemap.
• Do not tag links between pages of your own site. A tagged internal link can replace the original source of the visit in your reports.