What Changed
FLoC, short for Federated Learning of Cohorts, was Google's first proposal for interest-based advertising without third-party cookies. It grouped browsers with similar browsing histories into cohorts and shared a cohort ID with websites. After trials in 2021, it drew wide criticism: privacy groups such as the EFF argued the cohort ID was another stable signal that could help fingerprint users, and other browsers, including Edge, Firefox, Brave and Vivaldi, declined to support it.1,2
On January 25, 2022, Google announced that a new proposal, the Topics API, would replace FLoC.3 With Topics, the browser works out a handful of topics that represent a person's top interests each week, such as "Fitness" or "Travel & Transportation", based on their browsing history.
Topics are kept for only three weeks. When a person visits a participating site, the browser shares just three topics, one from each of the past three weeks, with the site and its advertising partners. Google said the topics are curated to exclude sensitive categories such as gender or race, and that Chrome would let users see and remove topics or turn the feature off.
Why It Mattered
Topics was Google's answer to a central question of the Privacy Sandbox: how to support interest-based ads without tracking individuals across sites. It gave much less information than cookies, by design: a few coarse categories rather than a detailed browsing profile.
It never had support beyond Chrome. Both Mozilla and Apple's WebKit team published formal positions against Topics, arguing that a browser shouldn't share data about a person's browsing from one site with another.4,5 Advertisers could reach Safari and Firefox users with neither cookies nor Topics.
That trade-off was the problem for adoption. Advertisers and ad tech companies tested Topics alongside cookies, and with cookies still available in Chrome, there was little reason to rely on a weaker signal. In October 2025 Google retired Topics on both Chrome and Android, citing low adoption.
Notes
- Bennett Cyphers, “Google’s FLoC Is a Terrible Idea,” Electronic Frontier Foundation, March 3, 2021, https://www.eff.org/deeplinks/2021/03/googles-floc-terrible-idea. ↩
- Dieter Bohn, “Nobody Is Flying to Join Google’s FLoC,” The Verge, April 16, 2021, https://www.theverge.com/2021/4/16/22387492/google-floc-ad-tech-privacy-browsers-brave-vivaldi-edge-mozilla-chrome-safari. ↩
- Vinay Goel, “Get to Know the New Topics API for Privacy Sandbox,” The Keyword, Google, January 25, 2022, https://blog.google/products-and-platforms/products/chrome/get-know-new-topics-api-privacy-sandbox/. ↩
- “Topics API,” Mozilla Standards Positions (GitHub), March 2022, https://github.com/mozilla/standards-positions/issues/622. Position: negative. ↩
- “The Topics API,” WebKit Standards Positions (GitHub), December 2022, https://github.com/WebKit/standards-positions/issues/111. Position: oppose. ↩