Where Did Your Visitors Actually Come From? A Practical Guide to GA4 Traffic Channels

ChatGPT ads reached Australia in 2026, and a handful of Sydney agencies are now testing them. Far fewer are talking about what happens after the click: how does that traffic actually show up in your reports?

When we ran our first test campaigns inside ChatGPT, we made an unforced error. We launched without UTM tags.

When we opened Google Analytics, our paid clicks weren't recorded as paid traffic at all. They had landed in GA4's newest channel: AI Assistant. So if you don't properly setup your UTM tags, your traffic will be placed inside GA4's Default Channel Groupings.

Key terms (the ones your technical team will use)

Session: One visit to your site. GA4 assigns a channel to each session.
Source: Where the visitor came from, e.g. google, facebook, chatgpt.com, newsletter.
Medium: The type of traffic, e.g. organic, cpc (paid click), referral, email.
Referrer: Information the browser passes on about the previous website. GA4 uses it when there are no tags on the link. Some apps and browsers strip it out.
UTM parameters: Tags added to the end of a link (utm_source, utm_medium, utm_campaign) that tell GA4 exactly where the visit came from. When present, they take priority over the referrer.
Auto-tagging: Google Ads adds its own click ID (gclid) to ad links, so GA4 can classify Google Ads traffic without UTMs. Other ad platforms don't get this treatment in GA4's channel rules.

How GA4 sorts your traffic

GA4 checks each session against a list of channel rules, in order. The first rule that matches wins.

Paid rules are checked first, then organic ones, then AI Assistant, then Referral, Email and the rest. If nothing matches, the session is labelled Unassigned.

Google maintains these rules and you can't edit them. You can, however, build a custom channel group if you want your own categories (more on that below).

The main channels explained

Organic Search Unpaid clicks from search engines such as Google, Bing, Yahoo and DuckDuckGo. This includes clicks from Google's AI Overviews and AI Mode. Google treats these as part of search, not as AI assistants.

Paid Search Clicks on search engine ads. Google Ads traffic is classified automatically when your Google Ads account is linked to GA4 and auto-tagging is on. For other search engines, the source must be a recognised search engine and the medium must look paid (for example cpc, ppc or anything starting with paid).

Organic Social and Paid Social

Organic Social: Unpaid links from recognised social sites such as Facebook, Instagram, LinkedIn, Reddit and X, or links tagged with a social medium like social.
Paid Social: Ads on social platforms. Unless the ad runs through Google Ads, GA4 only knows it's paid if you tag it with a paid medium such as paid_social or cpc. An untagged Meta or LinkedIn ad will usually show up as Organic Social.

Referral A normal link from another website, such as a blog or news article linking to you.

Email Visits where the source or medium is tagged as email.

AI Assistant (new in 2026) Google added this channel on 13 May 2026. It captures visits from standalone AI chatbots. Google's documentation names ChatGPT, Gemini, Deepseek, Copilot and Grok, and its launch announcement also named Claude. Google hasn't published the full list, and coverage of Perplexity hasn't been confirmed.

When GA4 recognises an AI assistant as the referrer, it automatically:

sets the medium to ai-assistant
sets the campaign to (ai-assistant)
places the session in the AI Assistant channel

Three things to know:

It's not retroactive. Before May 2026, the same visits were mostly reported as Referral. Year-on-year comparisons need care.
It rolled out gradually, so some properties started populating later than others.
ChatGPT tags many of its own links with utm_source=chatgpt.com, so you'll often see chatgpt.com as the source.

Direct GA4 couldn't find a source. This happens when someone types your URL, uses a bookmark, or clicks a link in an app or privacy-focused browser that strips the referrer. Treat Direct as "unknown", not "loyal customers".

Paid Other Traffic tagged with a paid medium (such as cpc) where the source isn't a recognised search, social, shopping or video site. This matters for ChatGPT ads, as explained below.

Unassigned GA4 recorded the session, but its tags didn't match any rule. High Unassigned numbers almost always mean someone used a custom or misspelt medium, or set a source without a medium.

GA4 also has channels for Display, Organic and Paid Video, Organic and Paid Shopping, Affiliates, Audio, SMS, Mobile Push Notifications and Cross-network (e.g. Performance Max). Google's channel definitions page lists them all.

How to keep your channel data clean

Tag every paid link before launch. This applies to any newer platform: ChatGPT ads, newsletter sponsorships, podcast show notes and so on. OpenAI confirms that UTM tags on ChatGPT ad landing pages carry through when people click.

Paid ChatGPT ads

utm_source=chatgpt
utm_medium=cpc
utm_campaign=your_campaign_name

With these tags, GA4 classifies the clicks as Paid Other. They won't appear under Paid Search, because ChatGPT isn't on Google's list of search engines. That's fine, the key point is that your paid clicks are now separate from organic AI Assistant traffic. If you want a dedicated "Paid AI" line, ask your analyst to set up a custom channel group.

Organic links (social bios, email signatures, newsletters) Use standard mediums: social, email, referral.

Avoid invented mediums GA4 can only classify mediums it recognises. A few examples:

Tagging	Where it lands	Why
`utm_source=chatgpt&utm_medium=cpc`	Paid Other	Paid medium, but not a recognised search or social source
`utm_source=chatgpt&utm_medium=chatbot_promo`	Unassigned	Medium matches no rule
`utm_source=partner_news&utm_medium=sponsored`	Unassigned	Medium matches no rule
`utm_source=partner_news&utm_medium=email`	Email	Standard medium

Agree on a short, shared naming list (cpc, paid_social, display, social, email, referral) and stick to it across the team and your agencies.

Questions to ask your technical team

Are all our paid links tagged with UTMs, including ChatGPT ads, sponsorships and partner placements?
Is Google Ads linked to GA4 with auto-tagging on?
How much of our traffic is Unassigned or Direct, and what's causing it?
Do we need a custom channel group to report paid AI traffic, or AI platforms Google doesn't yet recognise?
How are we handling year-on-year comparisons, given AI Assistant data only starts in May 2026?

Clean data doesn't happen after a campaign ends. It happens in the URL, before you press launch.

Need an honest review of where your acquisition data is going? Talk to Corsza. We'll audit your channels and make sure your marketing spend is measured accurately.

Sources

Google Analytics Help — Default channel group (official channel descriptions, rules and order): https://support.google.com/analytics/answer/9756891?hl=en
Google Analytics Help — Custom channel groups: https://support.google.com/analytics/answer/13051316
Google Analytics Help — Understand (direct) / (none) traffic: https://support.google.com/analytics/answer/15258820
OpenAI Help Center — Ads in ChatGPT: The Basics (UTM tags persist on ad clicks): https://help.openai.com/en/articles/20001207-ads-in-chatgpt-the-basics
Search Engine Journal — Google Analytics Adds AI Assistant As Default Channel Group: https://www.searchenginejournal.com/google-analytics-adds-ai-assistant-as-default-channel-group/574974/
Search Engine Land — Google Analytics now has an AI Assistant traffic channel: https://searchengineland.com/google-analytics-ai-assistant-477544
Louder (Australia) — ChatGPT Ads measurement in Australia: https://louder.com.au/2026/06/15/chatgpt-ads-measurement-in-australia/
Seer Interactive — How ChatGPT adds utm_source=chatgpt.com to links: https://www.seerinteractive.com/insights/are-ai-sites-like-chatgpt-sending-your-website-traffic