UA vs GA4 in 5 Minutes

GA4 is a major architectural update that affects many traffic and attribution metrics in some way. Big changes like this can be a bit overwhelming, so we’ve distilled some of the key differences for you here:

GA4 is Event-Based instead of Session-Based: In UA, sessions have events, while in GA4, events have sessions: Events and their attributes now contain all of the data that was previously contained by Sessions in UA. This has some big implications and capabilities, like rolling over sessions past midnight and the ability to carry sessions between apps and the web. Most numbers are going to change between UA & GA4 as a result of this architectural change. We recommend reading through some of Google’s documentation for more information on the differences between event-based and session-based architectures.
Conversion Events replace Goals, and can happen multiple times per session: There can now be multiple Conversion Events per session - if a “form submit” is a conversion event and a user submits multiple forms, multiple conversions will be registered. This can inflate CVR metrics if you’re not aware of this possibility during setup.
“Sessions” have many differences aiming to improve accuracy - A big effect on global brands is that sessions no longer reset at midnight. Sessions also carry across late hits (slow load times) for up to 72 hours. For more information on Sessions in GA4, see Google's documentation.
Attribution Overhaul - GA4 offers a new multi-touch attribution system called “Data Driven Attribution” which weighs advertising touchpoints using statistical methods and assigns credit based on their calculated importance. This is compared to last-click or first-click attribution, which assign all credit to just the first or last touchpoint. Legacy methods like Last Click can still be chosen in GA4 configuration, but Google now recommends “Data Driven Attribution” in setup.
Engagement Rate replaces Bounce Rate: GA4 introduces a new concept of "engaged sessions" which is in essence the inverse of "bounce rate" in UA. An engaged session is defined as a session in which the user has performed some meaningful interaction, such as clicking on a link, watching a video, or spending at least 10 seconds on the page.

If you’re aware of the above changes, you’ll have a reasonable sense of what to expect with GA4. For more information, check out the rest of our resources here!