The Rise and Fall of Google's Privacy Sandbox
For web privacy researchers and policymakers, this work provides empirical evidence that the Privacy Sandbox initiative failed to gain traction, leaving the challenge of privacy-preserving advertising unresolved.
The paper presents the first longitudinal, consent-aware measurement of Google's Privacy Sandbox APIs across the top 10,000 websites, finding that adoption stagnated before retirement, with most APIs used by only a few actors and activity declining steadily.
On October 17th, 2025, Google announced the retirement of most Privacy Sandbox APIs, concluding nearly five years of experimentation with its alternative to privacy-invasive data collection on the Web. Designed to balance privacy with advertising functionality and cross-site tracking, the initiative faced repeated redesigns and limited ecosystem support. In this work, we present the first longitudinal, consent-aware measurement of the Privacy Sandbox's deployment across the Web. Using a custom call listener and weekly crawls of the top-10,000 websites, we monitor the usage of all major APIs in the months preceding their retirement. Adoption had already stagnated well before Google's announcement: most APIs were used by only a handful of actors, whose activity declined steadily throughout our study. Even the APIs that Google plans to maintain show no sign of growth. The sole exception is Cookies Having Independent Partitioned State (CHIPS). Overall, the demise of the Privacy Sandbox leaves unresolved the challenge of enabling privacy-preserving interest-based advertising.