Data & identity · also called Google Privacy Sandbox
Privacy Sandbox
Privacy Sandbox was Google's initiative, launched in 2019, to build browser and Android APIs to replace cross-site tracking; in October 2025 Google announced it would retire most of those APIs.
Google announced the Privacy Sandbox in 2019 as a plan to support advertising without third-party cookies or cross-app identifiers. It proposed APIs that would do inside the browser, or on the Android device, what ad tech had done with tracking: the Topics API for interest-based ads, the Protected Audience API for remarketing auctions, the Attribution Reporting API for measurement, IP Protection and others.
The plan was tied to phasing out third-party cookies in Chrome, a timeline delayed several times and watched closely by the UK's Competition and Markets Authority. In 2024 and 2025 Google changed course and decided to keep third-party cookies in Chrome. Then, in October 2025, it announced it would retire most Privacy Sandbox technologies, including Topics, Protected Audience and Attribution Reporting on Chrome and Android, citing low adoption and ecosystem feedback.
A few pieces survived, such as partitioned cookies (CHIPS), federated login (FedCM) and Private State Tokens, which help anti-fraud. Privacy Sandbox's story is a key episode in signal loss debates and in antitrust in ad tech scrutiny of Google.
Think of it like this
Privacy Sandbox was like a plan to replace the city's old roads with a new tram system; after years of test tracks, the city kept the roads and dismantled most of the tram lines.
An example
An ad tech company that spent two years testing Protected Audience auctions in Chrome wound down that work in 2026 after Google's retirement announcement, redeploying engineers to first-party ID and contextual products.
Related terms
Topics API
The Topics API was a Google Privacy Sandbox feature that shared a few broad interests, inferred from recent browsing, with sites for ad targeting; Google announced its retirement in October 2025.
Protected Audience API
The Protected Audience API (formerly FLEDGE) was a Privacy Sandbox proposal to run remarketing ad auctions inside the browser without cross-site tracking; Google announced its retirement in October 2025.
Third-party cookie
A third-party cookie is a small file set in your browser by a domain other than the site you are visiting, typically ad tech, letting it recognise your browser across sites.
Cookieless advertising
Cookieless advertising means targeting and measuring ads without third-party cookies, using approaches like first-party data, contextual targeting, alternative IDs, clean rooms and modelled measurement.
Signal loss
Signal loss is the reduction in data available to target, measure and optimise advertising, caused by browser cookie blocking, mobile ID restrictions, privacy laws, consent choices and ad blocking.
Sources: Google: Update on plans for Privacy Sandbox technologies (October 2025), Google Privacy Sandbox