This article is about Google Analytics 4 properties. Refer to the Universal Analytics section if you're still using a Universal Analytics property, which will stop processing data on July 1, 2023 (July 1, 2024 for Analytics 360 properties).

[GA4] About connected site tags

This article is for website owners who are setting up a Google Analytics 4 property and who are given the option (by the setup wizard) to reuse their existing Universal Analytics tagging.

If your Universal Analytics property uses gtag.js, the GA4 Setup Assistant wizard can reuse your existing tagging (i.e., the tag being used by your Universal Analytics property). This tag reuse saves you from having to add the tag manually to your web pages and is made possible via a feature called connected site tags.

However, if your Universal Analytics property uses analytics.js, the GA4 Setup Assistant wizard won't be able to reuse your existing tag, unless your GA4 property was created automatically. You'll need to paste the Google tag (i.e., gtag.js) directly into your website pages.

The remainder of this article is for users with advanced implementation needs.

How it works

Here are a few points about how connected site tags work.

  • An additional gtag(‘config’, ‘G-XXXXX’) call is made (without any parameters), which downloads a Google Analytics 4 tag container and sends an automatic page_view event to the Google Analytics 4 property. 
  • Enhanced measurement events (when enabled) are automatically collected in the Google Analytics 4 property, but are not collected in the Universal Analytics property. 
  • Any events sent via gtag(‘event’) to the Universal Analytics property are also sent to the Google Analytics 4 property (except for events with a “send_to” parameter that only specifies the Universal Analytics property). 
  • Connected site tags require the full site to be consistently tagged using a gtag.js snippet that is controlled by a single Universal Analytics property. If your Universal Analytics property receives data from mixed implementations (e.g. some pages are tagged with analytics.js or Google Tag Manager), only the eligible pages will send data to the Google Analytics 4 property.


The connected Google Analytics 4 tag ignores any config parameters that customize data collection for the Universal Analytics property -- the connected Google Analytics 4 tag is fired without any config parameters. (Although Google Analytics 4 properties support many of the configuration parameters available for Universal Analytics properties,  these parameters have to be included in the config command in order to apply to the Google Analytics 4 property.) You can mitigate this issue by moving the parameters assigned in the gtag(‘config’) command for Universal Analytics to a gtag(‘set’) command before the gtag(‘config’) command.

Here are a few examples of how this can impact specific tagging controls for Google Analytics 4. Tag customizations (such as customized cookie settings, cross-domain linking, disabling advertising features, opting out from Analytics support for Google Ads conversions, and disabling GA measurement) that you may have set up for your Universal Analytics property in the gtag(‘config’) command are not  applied to your Google Analytics 4 property.  As a result, you may unintentionally collect the following in your Google Analytics 4 property:

Other caveats to note: 

  • User_id: The connected Google Analytics 4 tag will ignore any user_id that has been set in the Universal Analytics tag via gtag('config').
  • Pageview attributes: Custom pageview attributes such as page_title, page_location, and page_path will be disregarded in the connected site tag. This may result in data discrepancies between your Universal Analytics reports and Google Analytics 4 reports.

Add / remove custom site tags to / from a web data stream

After you create a web data stream, you can add connected site tags to the data stream and remove them when necessary (e.g., if you need to delete the data stream).

Add connected site tags

  1. In the Property column, click Data Streams.
  2. Click the row for the web data stream.
  3. Under Google tag, click Manage connected site tags.
  4. Under Connected Tags, enter the ID for the tag you want to add, then enter a name for the tag if you like.
  5. Click Connect.

Remove connected site tags

  1. In the Property column, click Data Streams.
  2. Click the row for the web data stream.
  3. Under Google tag, click Manage connected site tags.
  4. Under Connected Tags, in the row for the tag you want to remove, click More > Remove tag.

Scope of custom dimensions and metrics

Because there are differences between the Universal Analytics and Google Analytics 4 data models, your Google Analytics 4 data will look different from your Universal Analytics data. This is true regardless of whether or not you use connected site tags to implement your Google Analytics 4 property. 

For example, in Google Analytics 4 properties, custom event parameters and user properties replace Universal Analytics custom dimensions and metrics. When you use connected site tags, your Universal Analytics custom dimensions and metrics are automatically sent to your Google Analytics 4 property as custom event parameters. However, the scope of the custom dimensions/metrics, e.g. Hit-level scope, Session-level scope, User-level scope, and Product-level scope are ignored by the connected Google Analytics 4 tag, because the scope is set in the Universal Analytics user interface and requires the custom_map config parameter, neither of which is accessible to the connected Google Analytics 4 tag. As a result, custom metrics/dimensions do not persist to any scope beyond the event in an Google Analytics 4 property. This may not meet your needs for event collection and reporting, e.g. if you implement CRM integration by sending a user identifier (e.g., GA client ID or CRM ID) to Analytics as a user-scoped custom dimension. 

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