Guide 78 · Attribution · GA4 + Tag Manager
Default channel grouping in GA4: how every session gets one channel, and why Unassigned appears
GA4 sorts every session into one default channel from its source, medium and campaign. You cannot edit the rules, so the fix for a wrong channel is the tagging you send in.
After the trace, Traffic acquisition shows each session under one default channel, the rows add to the session total, and Unassigned is small enough to explain.
Download the reference: the default channel grouping reference (JSON) (651 bytes, MD5 2e9b89dccafda77d9a584c8b4f958c56). It holds the worked example from this guide with every figure recomputed. The file was built for this guide and checked the same day; it was not exported from a live property.
What you need
- Access to Reports, Acquisition, Traffic acquisition.
- A list of the UTM tags your campaigns use, so you can match a session to the rule that filed it.
- Editor access if you decide to build a custom channel group next to the default.
The trace
- Open Reports, then Acquisition, then Traffic acquisition. Keep the primary dimension on Session default channel group. That dimension is the default for the report.
- Read the channel rows as a rule-based filing, not as a guess. Google writes the rules from source, medium and campaign, and the default group cannot be edited. Direct, Organic Search, Paid Social, Organic Social and Email are among the groups the report names.
- Check the worked example in the download. For 1,840 sessions, Organic Search holds 612, Direct 438, Paid Search 291, Organic Social 204, Email 173 and Referral 122. The six rows add to 1,840. Organic Search is 33.3% of sessions and Direct is 23.8%.
- Trace one session back to its tag. A link tagged with a paid-search medium lands in Paid Search under the paid pattern, while the same landing page reached from a search engine with no tag lands in Organic Search. The channel follows the tag, not the page.
- Look at Unassigned last. Unassigned holds sessions that matched no rule. A large Unassigned row is usually a tagging problem on your side: a medium value Google does not recognize, or a campaign with no medium at all.
- If you need a different grouping, build a custom channel group in Admin, under Data display, then Channel groups. It starts from a copy of the default and applies to reports retroactively. Do not try to edit the default group; Google maintains it for all users.
Dead ends
DEAD END — EDITING THE DEFAULT GROUP. There is no edit control for the default channel group. The editable copy is the primary channel group, and custom groups sit next to the default.
DEAD END — READING ONE CHANNEL IN THREE DIMENSIONS AS ONE NUMBER. Session default channel group, First user default channel group and Default channel group answer different questions: session, user and key event. They will not match.
DEAD END — BLAMING GA4 FOR UNASSIGNED. Unassigned means no rule matched the source and medium that arrived. Check the link tags first, before assuming a GA4 fault.
End state
The worked example adds to 1,840 sessions across six channels. Organic Search is the largest at 612 sessions, 33.3%, and Referral is the smallest at 122. The default group is read-only, so a wrong channel is fixed by fixing the tag.
Sources
- Analytics Help — Traffic acquisition report — Session default channel group as the default dimension, and the named default groups including Direct, Organic Search, Paid Social, Organic Social and Email
Checked 11 November 2026. The click paths above are the ones in Google's help and developer pages, opened 11 November 2026. No step in this guide was run inside a live Analytics property or a live Tag Manager container, because both need a Google sign-in and this site does not sign in as anyone. The figures on this page were recomputed in Python 3 and are shown in the downloadable file, which was checked the same day. Google moves menu items without warning; if a path on this page no longer matches, the linked help page is the current map.