The GA4 Default Channel Group, Explained for Marketers
How GA4 assigns sessions to channels: the default channel group rules, the new AI Assistant channel, and how to fix Unassigned traffic.
GA4 assigns every session to a channel by checking its source, medium and campaign against Google's fixed rules, top to bottom. You can't edit those rules, but you can read them, tag to match them and build a custom group when they don't fit. The default group now includes an AI Assistant channel.
- Two versions exist: Session default channel group (per visit) and First user default channel group (first visit).
- Rules are based on source, medium, campaign and, for Google platforms, campaign or network type.
- The AI Assistant channel covers sources like ChatGPT, Gemini, Deepseek, Copilot and Grok; Google's AI Overviews and AI Mode count as Organic Search.
- Unassigned means no rule matched. It is almost always a tagging problem.
- The default group can't be edited. Custom channel groups can, and apply retroactively.
Checked 4 November 2026 (CET) against Google Analytics Help and Google developer documentation. GA4 menus and limits change, so confirm in your own property. "Our view" marks MentionX opinion. Ledgerline is a fictional company used for illustration.
01The channels and their rules (non-Google traffic)
This is a condensed version of Google's rules for manually tagged and referral traffic. Google's page has the full list, including Google Ads, DV360, CM360 and SA360 rules.
| Channel | Simplified rule |
|---|---|
| Direct | Source is (direct) and medium is (not set) or (none) |
| Cross-network | Campaign name contains cross-network |
| Paid Shopping | Shopping site source or shop campaign name, plus a paid medium |
| Paid Search | Search site source plus a paid medium such as cpc, ppc, retargeting or paid_* |
| Paid Social | Social site source plus a paid medium |
| Paid Video | Video site source plus a paid medium |
| Display | Medium is display, banner, expandable, interstitial or cpm |
| Paid Other | Paid medium, no other match |
| Organic Shopping / Social / Video / Search | Site lists or mediums such as social, video, organic |
| AI Assistant | Medium exactly matches ai-assistant; GA4 sets this when the referrer matches its list of AI assistants |
| Email, Affiliates, Referral, Audio, SMS, Mobile Push | Medium-based rules |
02What the AI Assistant channel changes
Google's help page says GA4 sets medium to ai-assistant and campaign to (ai-assistant) when the referrer matches its list of AI assistants. Two practical effects:
- Visits that used to appear as Referral from
chatgpt.comorperplexity.aimay now appear as AI Assistant. Expect a step change in Referral if you trend it over time. - Visits from Google's AI Overviews and AI Mode remain in Organic Search. GA4 can't separate them by referrer, so use Search Console (lesson 15 and what Search Console shows about AI Overviews).
Google does not publish the full assistant list on that page, and an assistant whose app strips the referrer still arrives as Direct. That is why the custom regex in lesson 7 is still worth having.
03How to fix Unassigned
- Open Reports → Acquisition → Traffic acquisition.
- Filter Session default channel group to Unassigned.
- Change the dimension to Session source / medium.
- Fix the template for each medium you see (lesson 5). Past data stays as it is; a custom channel group can relabel it.
Our view: treat channel numbers as directional. The rules are sensible, but referrer loss and consent mean Direct is always inflated.
Next: AI referral traffic: the AI Assistant channel and a custom regex. Or return to the GA4 for Marketers track.
04Common questions
Can I edit the GA4 default channel group? No. Google keeps one universal default. To change channel logic, create a custom channel group (lesson 7), which also applies to past data.
Why is traffic showing as Unassigned? Usually a UTM medium or source that matches no channel rule. Check Session source / medium for the Unassigned rows and fix your tagging template.
Is there an AI channel in GA4? Yes. Google's default channel group now lists an AI Assistant channel for sources such as ChatGPT, Gemini, Deepseek, Copilot and Grok. AI Overviews and AI Mode stay in Organic Search.
Questions people ask
3 answersCan I edit the GA4 default channel group?
+
No. Google keeps one universal default. To change channel logic, create a custom channel group (lesson 7), which also applies to past data.
Why is traffic showing as Unassigned?
+
Usually a UTM medium or source that matches no channel rule. Check Session source / medium for the Unassigned rows and fix your tagging template.
Is there an AI channel in GA4?
+
Yes. Google's default channel group now lists an AI Assistant channel for sources such as ChatGPT, Gemini, Deepseek, Copilot and Grok. AI Overviews and AI Mode stay in Organic Search.
Sources
- Google Analytics Help, Default channel groupsupport.google.com
- Google Analytics Help, Custom channel groupssupport.google.com
- Google Analytics Help, URL builders: Collect campaign data with custom URLssupport.google.com
- All accessed 4 Nov 2026.