In short. Standard GA4 properties have 2 custom groups, 360 properties have 5, and each group allows 50 channels.
Definition: A custom channel group is a set of rule-based channel categories for website traffic sources. Google documents a limit of 2 custom groups for a standard GA4 property and 5 for a Google Analytics 360 property, with 50 channels allowed in each group.
Key facts
- A standard property can have 2 custom channel groups in addition to the pre-defined channel group, according to Google's custom channel groups documentation.
- A 360 property can have 5 custom channel groups in addition to the pre-defined group. The 360 figure applies to subproperties and roll-up properties.
- Each custom group can contain 50 channels. Google lists the same per-group channel limit for standard and 360 properties.
- The default channel group is maintained by Google. The default channel group documentation says custom groups provide the rule-based categories that you can create for your own traffic taxonomy.
- Any custom group can become the property's primary channel group, which Google describes as the editable default used for future reporting.
What is included in the property limit?
As of October 2026, Google's per-property table counts custom groups separately from the pre-defined channel group. For a standard property, the documented allowance is 2 custom groups. For a 360 property, it is 5, and Google explicitly says the 360 limit applies to subproperties and roll-up properties. The table gives both property types a ceiling of 50 channels within each group.
The pre-defined group is a separate reference point for the property. Google's default-channel documentation says that default channel groups cannot be edited in Analytics and that custom groups let you create your own rule-based categories. An agency expanding its source taxonomy therefore needs to budget custom groups and channels, while keeping the default group as the documented baseline.
How should an agency expand its source taxonomy?
First compare the proposed source categories with the channels already provided by the default group. Google currently lists AI Assistant as a default channel for visits from sources such as ChatGPT, Gemini, Deepseek, Copilot, or Grok. The same definition excludes Google's AI Overviews and AI Mode. The default-channel page also lists Default channel group, Session default channel group, and First user default channel group as separate dimensions with event, session, and user scopes.
If a custom rule is still needed, Google documents these reporting fields for custom channel groups: campaign id, campaign name, default channel group, manual ad content, medium, source, and source platform. A custom group can be used as a primary dimension in Acquisition reports, as a secondary dimension in default reports, and as a dimension in custom reports and explorations. Google also says custom groups can be applied to reports retroactively.
For an assistant-source channel, the documentation gives this regex example:
^.*ai|.*\.openai.*|.*chatgpt.*|.*gemini.*|.*gpt.*|.*copilot.*|.*perplexity.*|.*google.*bard.*|.*bard.*google.*|.*bard.*|.*.*gemini.*google.*$
Google instructs you to place an AI Assistants channel above Referrals when the rules overlap, because traffic is included in the first channel whose definition it matches in the current group order.
What can you change when the group is full?
The limit concerns the number of groups and the number of channels within each group. Google documents editing existing channels, adding channels, removing channels, and reordering them. The setup is in Admin, under Data display and Channel groups, and Google requires the Editor role or above at the property level to create and edit channel groups.
If the taxonomy needs another view, a property owner can select any one custom group as the primary channel group. Google says that the selected criteria populate the primary channel group dimension on future reporting. The documentation also warns that creating a custom channel group with a large number of fields may negatively affect reports.
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?
- How do I make a custom channel group the primary group in GA4?
FAQ
Does the default channel group use one of the custom-group slots?
No. Google's table states that the 2 standard-property groups and the five 360-property groups are in addition to the pre-defined channel group.
Does Google Analytics 360 allow more than 50 channels in one group?
No higher 360 value is listed. The documented limit is 50 channels within each group for both standard and 360 properties.
Can the default channel group be edited to add a source?
Google maintains the default channel group. Create or edit a custom group for a separate rule-based category, or select a custom group as the primary channel group when that reporting definition is needed.
What should an agency check before adding another group?
Check the property's existing custom-group count, the channel count in the target group, and whether the default group already contains a suitable channel. Google documents the current AI Assistant definition and the first-match ordering rule for custom groups.
Sources
- Google Analytics Help, "Custom channel groups", undated
- Google Analytics Help, "Default channel group", undated
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