UID2: The Standard That Replaced the Cookie
The earlier post – The Cookie That Never Expires – showed how hashed email addresses became the ad industry’s replacement for the tracking cookie. Companies hash your address when you hand it over, and the hash becomes the identifier that follows you across sites and devices. That practice did not stay informal for long. In 2019, The Trade Desk gave it a name, a spec, and an open-source implementation. The result is called Unified ID 2.0, UID2 for short, and it is now the infrastructure underneath a significant share of the open web’s advertising.