Google's primary tag for Google Measurement/Conversion Tracking, Adwords and DoubleClick.
https://support.google.com/adwords/answer/7548399
Analytics and Tracking
Get access to data on 45,520,508 websites Global Site Tag Customers. We know of 22,384,431 live websites using Global Site Tag and an additional 23,136,077 sites that used Global Site Tag historically and 3,053,114 websites in the United States.
Get a list of 45,520,508 websites using Global Site Tag which includes location information, hosting data, contact details, 22,384,431 currently live websites and an additional 4,296,427 domains that redirect to sites in this list. 23,136,077 sites that used this technology previouslyand 3,053,114 websites in the United States currently using Global Site Tag.
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