UID2 (Unified ID 2.0)

Unified ID 2.0 is an open-source identity framework that turns an email address or phone number a user has consented to share into a pseudonymous identifier for programmatic advertising, so that publishers, advertisers and platforms can match audiences across the open web, apps and CTV without third-party cookies.

The framework's documentation describes it as providing "deterministic identity for advertising opportunities on the open internet," as a standalone solution with its own namespace, licensed under the Apache License 2.0, with publicly available source code, no centralized storage of mappings to directly identifying information, and a Transparency and Control Portal through which consumers can opt out (Unified ID 2.0 documentation, last updated 13 October 2026). The documentation is hosted in an IAB Tech Lab GitHub repository; The Trade Desk created the framework and its privacy pages are linked from the docs. The European variant is EUID.

Technically, a raw UID2 is derived from a normalised, hashed and salted email or phone number; a UID2 token is an encrypted form of the raw UID2 that a publisher puts into the bid request, and that only authorized DSPs can decrypt; tokens are refreshed through a token/refresh endpoint (Unified ID 2.0 documentation). In OpenRTB the token travels in user.eids with source set to the UID2 domain, and since the 2.6-202409 snapshot the EID object can also say who inserted it and how it was matched (openrtb2.x releases).

Example: "user": { "eids": [{ "source": "uidapi.com", "uids": [{ "id": "AgAAAJ…", "atype": 3 }] }] }. Optable reports that Triton Digital and iHeartMedia saw a 2.4x fill rate on UID2 traffic, a vendor case study (Optable).

Related: consent string, TCF, clean room, bid request.

Source: Unified ID 2.0 documentation (unifiedid.com); IAB Tech Lab, OpenRTB 2.6 EID object.

1. Unified ID 2.0 documentation
2. openrtb2.x releases
3. Optable