Some of the key differences between UA and GA4 are:

	UA	GA4
Data Model	Hits-based data model, which records every user interaction as a separate hit or request.	Event-based data model, which records user interactions as events, each with its own set of parameters.
Property Structure	One property per website/app, which contains multiple views.	One property per account, which contains multiple streams.
Data Collection	Tracking code, which is a snippet of JavaScript code that is added to web pages or mobile apps to collect data.	Measurement protocol, which is a set of rules and specifications for sending data directly to Google Analytics servers using HTTP requests.
Reporting	Custom reports, which are reports that are created by users and can be highly customized.	Custom reports + pre-built templates, which are reports that can be customized but also come with pre-built templates to make it easier to get started.
Segmentation	Advanced Segments, which are subsets of data based on specific criteria.	Segments + audience builder, which includes advanced segmentation capabilities along with an audience builder to create custom audiences.
Attribution	Last non-direct click model, which gives credit to the last non-direct source that a user interacted with before a conversion.	Multiple attribution models, which include data-driven attribution and other models to help assign credit to different touchpoints along the user journey.
User ID	Optional, allowing tracking of user behavior across multiple devices or sessions if implemented.	Required for cross-device tracking, allowing tracking of user behavior across multiple devices or sessions.
Enhanced Ecommerce	Plugin for tracking ecommerce data, which requires additional implementation.	Native support for tracking ecommerce data, which simplifies the implementation process.
Machine Learning	Limited machine learning capabilities, such as automated insights and anomaly detection.	Advanced machine learning capabilities, including predictive metrics and smarter insights.

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