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Hi @salmon-policeman-87046 the tracking-key I use it as a experiment ID. To your questions: 1. You need to write your own code so the anon ID is set in the growthbook UserID attribute. Usually you have to also check on about Cookie consent etc. but It might not sound sexy but a polling technique to check for the GA anon ID works fine also from performance perspective. _ga is the name of the cookie you are looking for. 2. When the trackingCallback fires (happens automatically when an experiment is launched) the growthbook will do a datalayer push which contains the tracking-key and the variation id. Then you would need a GTM tag that retrieves this from the datalayer and sends it to GA4. 3. See attachement