Identity & Privacy

Why identity matters

Almost everything ad tech does well depends on recognizing the same user across sessions:

• targeting Match a campaign to people who fit an audience segment.
• frequency Cap a user at 3 exposures per day — across sites and devices.
• attribution Link a viewed ad to a downstream visit, install, or purchase.

Without a stable identifier, all three become probabilistic at best. CPMs for "unknown" users drop 30–60%.

The third-party cookie

For 25 years a tiny browser cookie set by a domain other than the one you were visiting let ad-tech vendors recognize the same browser across the open web. It was the substrate for retargeting, frequency capping, and most cross-site measurement.

Safari (ITP) and Firefox (ETP) blocked it years ago. Chrome — ~65% of the web — was on a multi-year deprecation path; in 2024 Google pivoted to a user-choice model, but the cookie's practical signal value has been collapsing all along.

The three eras

1. era 1 · ~1998 – 2018
   Cookie era

   Third-party cookies sync IDs across DSPs/DMPs. Cross-site retargeting works out of the box.

2. era 2 · ~2018 – now
   Transition

   Mobile IFAs (IDFA, GAID), GDPR/CCPA consent, ATT prompts. Match rates fall, IDs fragment.

3. era 3 · emerging
   Cookieless

   Email IDs (UID2, RampID), browser cohorts (Topics), contextual, clean rooms, SDA, MMM.