channel grouping
Also called: default channel grouping, channels, default channel group
A channel grouping is a set of rules that sorts incoming traffic into named channels such as Organic Search, Direct, Paid Search, Referral, and Email, based on each visit's source and medium. In GA4 the default channel group is fixed; custom channel groups let you define your own.
How GA4 assigns a channel
Every session carries a source (where it came from, e.g. google) and a medium (how it arrived, e.g. organic). GA4 checks these against a fixed list of rules, in order, and files the session under the first channel that matches. A visit with source = google and medium = organic becomes Organic Search; source = (direct) with medium = (none) becomes Direct; a UTM-tagged newsletter link becomes Email. When nothing matches, GA4 labels the session Unassigned, which is a sign your tagging is broken, not a real channel.
The default channel group is universal and read-only, so Google can keep the definitions current across every property. If the built-in buckets do not fit your business, you build a custom channel group with your own rules and can set it as your primary channel group. Channel data also exists at three scopes: event, session (Session default channel group), and first user (First user default channel group), which matters when you separate first acquisition from re-engagement.
In May 2026 Google added an AI Assistants channel that groups referrals from assistants like ChatGPT, Gemini, and Copilot under the medium ai-assistant. It is not retroactive, and much AI traffic still arrives with no referrer and lands in Direct, so the channel undercounts real AI-driven visits.
How it affects your traffic
An SEO audit leans on channel grouping to prove where organic traffic actually comes from and where it leaks. A high Unassigned bucket or bloated Direct usually means broken UTM tags or missing referrers, which quietly deflates your reported Organic Search and hides real wins. Reading the channels also isolates the new AI Assistants traffic, so you can see whether AI search sends real visits before you invest in it. Our SEO Audit checks your channel definitions and tagging first, so the rest of the numbers you act on can be trusted.
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