Default channel grouping
Default channel grouping is a derived dimension that maps each visit's source, medium, and campaign onto a fixed set of channels — Organic Search, Paid Search, Direct, Email, Referral, and more. GA4 applies an ordered set of rules at query time, so a visit only gets a channel if it matches the rule's source/medium pattern. Misclassification almost always traces back to untagged or mistagged campaigns.
What this means
A channel is a named bucket of traffic — Organic Search, Paid Search, Direct, Email, Referral, Organic Social, and others. GA4 builds it by matching each visit's source, medium, and (for paid) campaign against an ordered list of definitions. The first rule that matches wins, so order is part of the definition.
Because it is rule-derived, channel grouping is only as good as the inputs: a session tagged utm_medium=email lands in Email; an untagged newsletter click that arrives with no referrer lands in Direct instead.
Where it breaks
Custom mediums that do not match any rule fall into 'Unassigned'. Paid channels depend on the medium being one of the recognised paid tokens (cpc, ppc, paid) — a misspelled medium silently drops out of Paid Search. And the default rules differ from Universal Analytics, so historical comparisons across the GA4 migration are not like-for-like.
- Ordered rules: first match wins
- Unrecognised medium => Unassigned
- Paid detection depends on cpc/ppc/paid tokens
How it appears in analytics and logs
A channel value is the outcome of GA4's ordered rule set applied to source/medium/campaign. A large 'Unassigned' or 'Direct' bucket usually means tagging gaps, not a real channel shift.
Diagnostic use case
Use channel grouping for a high-level traffic mix, while remembering the channel is computed from source/medium rules and that 'Unassigned' flags traffic those rules could not place.
What WebmasterID can help detect
WebmasterID rolls referrer + utm_* into channels at ingest, and surfaces an explicit AI-referral channel so assistant traffic is not buried inside Referral or Direct.
Common mistakes
- Treating 'Unassigned' as a real channel instead of a tagging gap.
- Assuming GA4 channel rules match Universal Analytics.
- Using a custom medium token that no channel rule recognises.
Privacy and accuracy notes
Channel grouping is derived from referrer and campaign tags, not from cross-site identity. WebmasterID groups channels first-party and never infers them from fingerprinting.
Related pages
- Source / medium: the core traffic-origin dimension
Source/medium is the dimension that records where a visit came from (the source, e.g. google) and how it arrived (the medium, e.g. organic). It is derived from the referrer and UTM parameters, with rules that vary by tool. The big caveat: when neither is available, the visit lands in 'direct / (none)', which is a catch-all, not a channel.
- Session default channel grouping
Session default channel grouping rolls a whole session's source/medium into one channel — Organic Search, Email, Referral — based on the origin captured at session start. It is the session-scoped sibling of the user-scoped 'first user' channel and the event-scoped channel. GA4 offers several channel dimensions at different scopes, and mixing them is a leading cause of attribution numbers that do not reconcile.
- Referrer grouping into channels
Analytics platforms do not report every raw referrer separately — they map hosts into channel groups such as organic search, paid, social, referral, email, and direct. Understanding the default rules explains why a click ends up in one bucket versus another, and why a custom source can be misfiled until you adjust the grouping.
- Attribution analytics
Channel-level attribution across AI, search, and referral.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.