Protected Audience API

Protected Audience aimed to keep retargeting alive without third-party cookies. When you visited an advertiser's site, the browser could add you to an "interest group" stored on your device. Later, on a publisher's site, the browser itself ran an auction among interest-group ads and contextual bids, choosing a winner without revealing to the publisher or advertiser who you were or where else you had been.

The design involved on-device bidding logic, trusted key-value servers, "fenced frames" to render winning ads in isolation and aggregated reporting. It was ambitious but complex, adding latency and requiring major changes to DSP, SSP and ad server systems. The UK CMA also scrutinised how it might favour Google's own ad tech.

Testing in 2024 and 2025 showed limited adoption and performance concerns. When Google decided to keep third-party cookies, the rationale faded, and in October 2025 it announced it would retire Protected Audience on Chrome and Android along with most of the Privacy Sandbox.

Think of it like this

Protected Audience was like holding an auction inside your own home, where bidders send sealed envelopes and only the winning poster goes on your wall, and nobody learns your address.

An example

During 2024 tests, a travel advertiser added visitors to a "Paris hotels" interest group; weeks later, Chrome ran an on-device auction on a news site and showed the advertiser's Paris offer.