EID object
An EID groups one or more user IDs from a single identity source, such as a universal ID provider, inside the user.eids array. It names the source by domain, and since 2.6-202409 it can also record who added the ID and how the match was made, so buyers can judge how far to trust it.
How it is used
EID arrived as a first-class object in OpenRTB 2.6, replacing the user.ext.eids convention. The exchange should send only IDs that its agreements and the request's consent signals allow. Buyers usually support a short list of sources and ignore the rest, so source must match the domain the provider publishes exactly.
The User identity and EIDs page covers it in more depth.
Fields
Where it sits
Contained in: User.
Contains: UID.
All objects
The field reference index lists every OpenRTB 2.x object.