Acquisition reports and channel groups

The Acquisition collection answers "where did people come from". It has two detail reports that look alike and are easy to confuse:

• User acquisition uses user-scoped dimensions: First user source, First user medium, First user default channel group. They describe how a user was acquired the first time ever, so a visitor who found you via Google a year ago and returned from an email today is still counted under Organic Search here.
• Traffic acquisition uses session-scoped dimensions: Session source / medium, Session default channel group, Session campaign. Each session is credited to the source that started it, so today's email visit is Email.

Use user acquisition to judge which channels bring new people, and traffic acquisition to judge which channels drive visits and key events now.

A default channel group is a rule-based bucket derived from source, medium and campaign: Direct, Organic Search, Paid Search, Organic Social, Paid Social, Email, Referral, Affiliates, Display, Cross-network, Organic Video, Paid Video, Organic Shopping, Paid Shopping and a few more. Unassigned means GA4 saw source/medium values that matched no rule, which almost always means a non-standard utm_medium. You can define up to two custom channel groups in Admin for your own buckets, without changing the default.

Direct means no referrer and no campaign parameters: typed URLs, bookmarks, untagged emails, many mobile apps and some privacy-stripped referrers. A large Direct share is usually a tagging gap, not loyal fans.

Typical columns: users or sessions, engaged sessions, engagement rate, average engagement time, key events and session key event rate.