In short. Select a custom group through the pencil icon in Admin > Data display > Channel groups to apply its rules to future primary channel group data.
Definition: A channel group classifies website traffic sources into channels using rules. In Google Analytics 4 (GA4), selecting a custom channel group as the property's primary channel group makes its rules populate the primary channel group dimension from that point forward.
Key facts
- As of October 2026, Google's custom channel groups documentation places the primary setting at the top of the Channel groups admin page, behind a pencil icon.
- Google's default channel group documentation describes the primary channel group as the property's editable default; Google maintains the predefined default channel group.
- Google's Traffic acquisition report documentation describes session dimensions as covering both new and returning users.
Where is the primary channel group setting?
Google's custom channel groups instructions give this admin path:
Admin > Data display > Channel groups
Creating and editing channel groups requires the Editor role or higher at property level. The property selector changes which property's channel groups are displayed.
At the top of the Channel groups page, the pencil icon opens a panel for selecting a custom group as the primary group's definition. The selected group's criteria then populate primary channel group values going forward.
If a custom group is needed first, Create new channel group starts with a copy of the default group. Existing groups also offer Copy to create new. After editing the channels and their order, Save group saves the group. Traffic enters the first channel whose rules it matches.
Does changing the primary group rewrite historical reports?
Google's primary channel group guidance states that data uses the selected criteria from the change onward. Initially, the primary group uses the same definition as the Default Channel Group. Selecting a custom group changes the rules used for future primary channel group reporting.
The same documentation separately allows custom channel groups to apply retroactively in reports. Editing a custom group immediately applies its new definition to underlying data in reports, explorations and segments. A custom group selected directly in a report therefore supports historical reclassification, while the primary dimension preserves the grouping used over time.
How does this relate to report dimensions?
Google's default channel group explanation distinguishes Session default channel group, which describes how sessions begin, from First user default channel group, which describes how users first arrive. The predefined default group remains maintained by Google and cannot be edited.
Google's Traffic acquisition guide gives this report path:
Reports > Acquisition > Traffic acquisition
Its dimensions include Session source / medium, the source and medium associated with a new session. Its Sessions metric counts sessions that begin on the website or application.
Google's custom channel group guide also allows a custom group as the primary dimension in Acquisition reports, or as a secondary dimension in default reports. This report-level choice is available independently of selecting the property's primary channel group in Admin.
Related terms
- How do I create an AI assistants channel in GA4?
- Why does GA4 custom channel rule order affect AI traffic classification?
- Can a GA4 custom channel group classify historical visits?
- GA4 traffic acquisition
FAQ
Can I make an existing custom group primary?
Yes. Google's custom channel groups documentation allows any single custom channel group to supply the primary group's definition through the pencil control in Admin.
Must I make a group primary to use it in a report?
No. The same documentation allows you to select a custom group directly as a primary or secondary report dimension, including in Acquisition reports.
Sources
- Google Analytics Help, "Custom channel groups", undated
- Google Analytics Help, "Default channel group", undated
- Google Analytics Help, "[GA4] Traffic acquisition report", undated
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