What is a channel group?
A channel group classifies traffic into rule-based categories such as Organic Search, Referral and Direct so their recorded behavior can be compared.
The source can name a platform or website. The medium describes a traffic type, such as organic or referral. The channel applies broader classification rules to that information.
Check the dimension's scope before comparing
Session default channel group concerns the source of a session. First user default channel group concerns how a user first arrived. A user can return through another channel, so the two dimensions need not produce the same distribution.
State which dimension you used and keep it consistent across the comparison. A similar-looking channel label does not make different scopes interchangeable.
Four channels that are often confused
AI Assistant
Groups recognized visits from AI assistants such as ChatGPT, Gemini, DeepSeek, Copilot and Grok under Google's documented rules. It excludes Google AI Overviews and AI Mode. It also does not count a crawler fetching a page.
Referral
Describes non-ad traffic from links on other sites or apps. It is a defined category, not a guarantee that every external click will appear there.
Direct
Can include visits without a clear source, including directly entered URLs and visits whose source information was lost or unavailable. It cannot all be assigned to deliberate brand demand or retroactively counted as AI traffic.
Organic Search
Includes traffic from non-ad search results, including Google's AI Overviews and AI Mode under the cited documentation. That classification differs from visits from a standalone assistant.
What can the classification establish?
It describes the recorded visit under a rule set. It does not reveal the full pre-visit journey, establish an AI citation or measure whether a crawler used the content.
The AI referral measurement guide explains how to inspect the recorded sources and later actions together. Keep any missing-source limitation alongside the result.
Sources and scope
Source-language entry records a source check on 2026-09-28. Google’s default channel definitions were reopened on 2026-10-26. The Direct explanation otherwise retains the original entry’s recorded scope.