Here are the critical differences between GA4 and UA: #1. Google Analytics 4 uses an event-based measurement model vs a session-based model used by Universal Analytics. #2. Google Analytics 4 has no data limits vs 200,000 hits per day in Universal Analytics. #3. Google Analytics 4 measures some actions by default without needing to install tags. #4. Google Analytics 4 was created to track users across different devices and websites. #5. Google Analytics 4 offers AI and Machine Learning solutions for free. #6. Google Analytics 4 is highly customisable, and you can set it up for your needs. #7. Google Analytics 4 can be integrated with BigQuery, and you can analyse your data using SQL for free. #8. Google Analytics 4 allows you to organise your data better to suit GDPR and CCPA.