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Key event

A key event is a Google Analytics 4 event, such as a purchase, that you mark as important so GA4 reports it separately and Google Ads can import it.

How it works

GA4 records every action on the site as an event: a page view, an add to cart, a purchase. You can mark any event as key, and some, such as purchase, are key by default. Until 2024 GA4 called key events conversions. The mark applies from that moment on.

A key event reaches Google Ads only when you import it from the linked GA4 property; until then it stays hidden there. Once imported, it works as an ordinary conversion action. GA4 and Google Ads each apply their own attribution settings to the same purchases, so their numbers can differ. Which source Shopping and Performance Max should learn from is the subject of GA4 key event import vs the Google Ads tag.

Where you see it

  • GA4 reports: the Key events metric and the Is key event dimension.
  • Google Ads: the imported action in the conversion action list.
  • The portal’s conversion check, when an analytics import and a tag both count one order as primary goals.

Example

Example store, not client data.

The tableware shop has 300 orders a month on 40,000 of spend. Its Google Ads tag records every purchase, and the shop also imports the GA4 purchase key event. With both actions primary, Google Ads counts 300 + 300 = 600 conversions, and the cost per conversion falls from 133 to 40,000 ÷ 600 = 67. The shop still has 300 orders.

Not to be confused with

  • Primary conversion action — a Google Ads status that puts an action into the Conversions column and into bidding. It is set on the imported action, not by marking an event as key in GA4.

Right and wrong readings

  • Wrong: “We marked add_to_cart as key today, so last month’s report now includes it.” Right: the report stays as it was, because marking does not change historic data.
  • Wrong: “Purchase is a key event in GA4, so Google Ads bids on it.” Right: it enters bidding only once imported and set as primary, or added to a custom conversion goal.

Sources

  • API dimensions and metrics — Google Analytics Data API: Key events and Is key event; historic data unchanged; purchase is key by default. Checked 2 October 2026.
  • Changelog — Google Analytics Admin API, 6 May 2024: KeyEvent replaces ConversionEvent. Checked 2 October 2026.
  • Getting started — Google Ads API: Analytics conversions not imported into Google Ads are hidden. Checked 2 October 2026.
  • Conversion goals — Google Ads API: primary actions are used in bidding and reported in Conversions; custom conversion goals. Checked 2 October 2026.