Proposals in the Privacy Sandbox follow the idea of k-anonymity and are based on advertising to groups of people called cohorts instead of tracking individuals.

[2]: 41  There are three focuses within the Privacy Sandbox initiative: replacing the functionality of cross-site tracking, removing third-party cookies, and mitigating the risk of device fingerprinting.

Google is developing such a framework in cooperation with the CMA and is seeking to drive engagement with market participants on the design of testing between now and at least the beginning of General Availability in Q3 2023.

[36] Multiple media outlets and privacy advocacy groups criticised Google's decision to enable the feature by default for all users during the testing phase.

[43][44] Mozilla pointed out flaws in the Topics API's design, highlighting that it could allow large advertising networks to reidentify and track users by aggregating their interests across numerous websites.

[45] Apple echoed similar concerns, also noting that the proposal contradicted efforts made by other browsers to partition data on a per-site basis.

[46] Furthermore, when the proposal was initially announced, there were uncertainties about how Google or other browser vendors would establish a taxonomy of topics, a critical aspect of the API that was left underspecified.

Consequently, in January 2021, the Competition and Markets Authority (CMA) in the United Kingdom announced plans to investigate the Privacy Sandbox initiative, with a focus on its potential impacts on both publishers and users.

[48] CMA subsequently accepted legally binding commitments offered by Google concerning its proposals to remove third party cookies on Chrome and develop the Privacy Sandbox.