What it means
GA4 (Google Analytics 4) is the current generation of Google Analytics. It replaced Universal Analytics in mid-2023. Where Universal Analytics was session-based and pageview-centric, GA4 is event-based: every interaction (page view, click, scroll, video play, custom event) is a discrete event, which makes it easier to model modern multi-step user journeys.
GA4 also includes free BigQuery export, machine-learning-based predictive metrics, and built-in cross-device user identification, all of which were paid add-ons in the previous generation.
Why it matters
If you are running ads, you almost certainly need GA4 for closed-loop reporting. It is the canonical place for cross-channel attribution: which ads drove which website behaviour, which behaviour led to conversions.
Setup matters. Default GA4 captures a lot but misses business-specific events (custom button clicks, form submissions, conversion thresholds). A clean GA4 setup with custom events configured through GTM is the difference between vague directional data and an actual decision-making tool.
Example
An e-commerce brand migrates from Universal Analytics to GA4, configures custom events for cart-add, checkout-start, and purchase-complete via GTM, and connects GA4 to BigQuery. Six months later, they spot a checkout drop-off pattern in BigQuery that GA4's standard reports never surfaced. They fix one form field, recover 8 percent of abandoned carts.