GA4

GA4 is the current version of Google Analytics, built on an event-and-parameter data model rather than the session-and-pageview model of Universal Analytics.

Every interaction is an event in this model, including a page view; sessions are still reported but are derived, not the underlying storage unit. A new concept is the engaged session: one that lasts at least ten seconds, includes two page views or reaches a key event. This is where the sharpest definition collision sits, because bounce rate in this version means one minus engagement rate and is not comparable with the previous version's bounce rate, which invalidates historical comparisons and any reference figure published before the change. Collection has its own defaults too: exploration reports apply sampling and thresholding to small groups.