Session-Scoped vs. Event-Scoped Attribution
Google Analytics 4 introduced significant changes to how UTM parameters are processed and attributed. Understanding these changes is critical for accurate reporting.
In GA4, UTM parameters are captured at the session level, not the event level. This means:
sessionSource / sessionMedium / sessionCampaign — The UTM values from the session's first touch
firstUserSource / firstUserMedium — The UTM values from the user's very first visit
The Data-Driven Attribution Model
GA4 defaults to a data-driven attribution model that uses machine learning to assign credit across multiple touchpoints. This is different from Universal Analytics' last-click model.
Reading UTM Reports in GA4
To view UTM performance in GA4:
Go to Reports > Acquisition > Traffic Acquisition
Use the Session source / medium dimension
Filter by specific campaigns using the search bar
