It sits between Source platform and Source/Medium: broader than channel groupings, but less granular than source/medium.
Source group is based only on the source, so paid and organic traffic are combined (e.g. both paid and organic Instagram traffic appear as “Instagram”).
At the same time, Source platform is being updated to recognize third-party ad platforms.
If the source is a known platform and utm_medium indicates paid traffic, GA4 assigns the corresponding platform (e.g. instagram + utm_medium=paid → Source platform = “Meta Ads”). Otherwise, Source platform will show Unlabeled.
The new dimension is rolling out gradually and will be applied retroactively in Advertising reports.
Thanks for sharing Tamás Geiger
