What's the difference between Google Analytics and Google Analytics 4?

Google Analytics 4 (GA4) is the newer version replacing Universal Analytics. Key differences include event-based tracking (GA4) vs session-based (UA), better privacy compliance, cross-platform tracking (web + app), machine learning insights, and different reporting interface. GA4 uses events for everything, making it more flexible but requiring different setup. GA4 focuses on user journeys across devices. Universal Analytics stopped processing data in July 2023, so GA4 is now required. Migration involves setting up GA4, running both in parallel, and learning the new interface. Many consultants help with GA4 migration and setup, as the new interface requires learning.