GA4 Dimensions and Metrics Reference: What Changed in 2025 to 2026
GA4 is not a static platform. Google regularly deprecates, renames, and adds dimensions and metrics, often with limited notice. If you rely on any custom reporting or BigQuery exports, these changes can silently break your dashboards or produce incorrect data.
Key dimension changes
- Session source/medium consolidation: GA4 consolidated several traffic source dimensions. The "Session default channel grouping" replaced the older "Default channel grouping" for session scoped attribution. Reports using the old dimension name in Looker Studio connectors or the API now return errors or empty data.
- First user dimensions: GA4 added "First user source", "First user medium", and "First user campaign" as user scoped attribution dimensions. These reflect the traffic source at first visit, persisting across sessions. Existing reports using "User first touch channel" may need updating to use the newer dimension names.
- Content group dimensions: Content groups were renamed from "contentGroup" to "content_group" (and associated numbered variants) in the API. Any Measurement Protocol or API queries using the old naming convention will need updating.
Metrics that changed behaviour
- Engaged sessions: The threshold for an "engaged session" (10+ seconds, 2+ page views, or a conversion event) has remained stable, but how GA4 counts sessions with cross domain tracking improved. Sessions previously counted twice when crossing domains now correctly count as one engaged session in most configurations.
- Revenue metrics: GA4 now separates "Total revenue" (all revenue events) from "Purchase revenue" (purchase events only) more clearly in the UI. If your Looker Studio reports were built on "Revenue" as a generic metric, verify which definition they're using to ensure you're comparing like for like.
How to stay ahead of changes
Monitor Google's GA4 release notes and the Data API changelog. When building dashboards, prefer API field names over display names since display names change more frequently.
Use the GA4 Dimensions and Metrics Explorer (available in the GA4 help documentation) to verify current field names before building critical reports.
For BigQuery exports, build a schema validation step into your pipeline that alerts you when expected columns are missing or renamed.
A GA4 audit that checks your property configuration and data quality can flag broken custom dimension registrations before they affect reporting.
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