Google Analytics 4 (GA4)

Google Analytics 4 (GA4) is Google's event-based analytics platform that superseded Universal Analytics in July 2023. Unlike its predecessor which relied on session-and-pageview-centric tracking, GA4 uses an event-driven data model that unifies web and app data into a single property.

Category: Analytics (also: General)

Author: Atomic Glue Analytics Team

## Definition

Google Analytics 4 (GA4) is the current generation of Google's web and app analytics platform, launched in October 2020 and made mandatory when Universal Analytics stopped processing data on July 1, 2023. GA4 replaces the session-and-pageview-based model of Universal Analytics with a fully event-driven data model. Every interaction a user takes (page load, click, scroll, purchase, video engagement) is recorded as an event, each carrying typed parameters. This model allows for cross-platform measurement, machine learning-powered insights, predictive metrics like purchase probability, and a privacy-first architecture that reduces reliance on third-party cookies. GA4 properties use data streams (web, iOS, Android) instead of the old view/property hierarchy, and introduces concepts like engaged sessions, engagement rate, and key events (formerly conversions).

## Event-driven data model

In GA4, everything is an event. There are four categories: automatically collected events (page_view, first_visit, session_start), enhanced measurement events (scroll, outbound click, site search, video engagement), recommended events (add_to_cart, purchase, login, sign_up with prescribed parameters), and custom events you define yourself. Each event carries parameters that act as typed dimensions or metrics. This is fundamentally different from Universal Analytics where pageviews, events, and transactions were separate hit types with different limits.

## Key differences from Universal Analytics

Universal Analytics counted pageviews and sessions using a last-click attribution default. GA4 counts events and uses machine learning for attribution modeling. UA had views and properties; GA4 has data streams. UA's bounce rate was a session with one pageview and no interaction; GA4's bounce rate is simply the inverse of engagement rate. UA had goals with a single configuration; GA4 uses key events with flexible counting. UA data was sampled heavily in reports; GA4 applies sampling less aggressively but still samples in explorations. UA used a tracking ID (UA-XXXXX); GA4 uses a measurement ID (G-XXXXXXX).

## Reporting and analysis

GA4 organizes reporting into Lifecycle (acquisition, engagement, monetization, retention) and User collections. The Reports snapshot gives an executive overview. The Explore section (formerly Analytics) provides free-form analysis with techniques like Segment Overlap, Cohort Analysis, Funnel Analysis, and Path Exploration. GA4 also surfaces AI-generated insights automatically, including trend changes, anomaly detection, and predicted metric values.

## Limitations and considerations

GA4 has no view-level data filtering like Universal Analytics. Raw data export to BigQuery is available only on the 360 tier or if you pay for the standard BigQuery export connection. Data retention defaults to 2 months (upgradable to 14 months). GA4's user interface has a steeper learning curve, and many standard reports that existed in UA (like the full Site Content report) have no direct equivalent. Session counting differs from UA: GA4 does not reset sessions at midnight, and session timeout is configurable but defaults to 30 minutes.

## Note

GA4 is still actively developed. Features like advanced segment application, custom channel groupings, and certain exploration templates continue to be added. Misconception: GA4 does not automatically track everything for you. Enhanced measurement handles common interactions, but complex tracking still requires implementation via Google Tag Manager or gtag.js.

## In code

// Sending a custom event with parameters via gtag.js
gtag('event', 'add_to_cart', {
  currency: 'USD',
  value: 29.99,
  items: [
    {
      item_id: 'SKU_12345',
      item_name: 'Organic Cotton T-Shirt',
      item_category: 'Apparel',
      quantity: 1
    }
  ]
});

## Common questions

Q: Is GA4 really better than Universal Analytics?

A: Better depends on your needs. GA4 is superior for cross-platform measurement (web + app in one property) and its event model is more flexible. But it lost reporting features that UA power users relied on, like view-level filters and full page-path reports. The real answer: GA4 is the only option available, so make it work for you.

Q: Does GA4 affect my data if I haven't migrated?

A: If you never set up a GA4 property alongside your UA property before July 2023, you lost your historical data. UA stopped processing new data on July 1, 2023. Any historical UA data that was not exported is accessible through the UA interface for a limited time but no longer collects new data.

Q: Can I run GA4 and UA at the same time?

A: Not anymore. UA stopped processing new hits on July 1, 2023. You can still access historical UA data in the old interface for a limited period, but dual collection is no longer possible.

## Key takeaways

• GA4 is an event-based analytics platform, not a pageview-based one
• Cross-platform tracking (web + app) happens in a single property
• The user interface and reporting structure are completely different from UA
• Enhanced Measurement covers basic interactions, but advanced tracking needs implementation
• GA4 offers predictive metrics and deeper integration with Google Ads and BigQuery

## Related entries

• [Event Tracking](atomicglue.co/glossary/event-tracking)
• [Session](atomicglue.co/glossary/session)
• [Pageview](atomicglue.co/glossary/pageview)
• [Google Tag Manager](atomicglue.co/glossary/google-tag-manager)
• [KPI](atomicglue.co/glossary/kpi)

Last updated July 2026. Permalink: atomicglue.co/glossary/google-analytics-4-ga4