At the start of 2021, Google offered the Federated Learning of Cohorts (FLoC) as a replacement for third-party cookies used to place relevant ads on sites. Following criticism and feedback over the past year, Google today proposed the Topics API as a new solution.
Google wants to phase out the use of third-party cookies in Chrome by 2023. To do so, it’s working on a series of privacy-preserving alternatives under the Privacy Sandbox banner. FLoC was the most attention-grabbing effort, and it involved clustering “large groups of people with similar browsing patterns” into a “cohort” created by on-device machine learning algorithms that analyze web history. Thanks to federated learning, the actual list of URLs visited by users does not leave their browsers.
FLoC was also criticized due to concerns that it could still be used to track users. WordPress and Amazon turned it off, while no other browser pledged adoption.
Google is now replacing its FLoC proposal with the Topics API after “widespread community feedback” from the trial period. The Topics API works by having your browser (Chrome) — in an on-device manner — determine topics that “represent your top interests for that week based on your browsing history.” Chrome will “leverage a classifier model to map site hostnames to topics.”
For each week, the user’s top 5 topics are calculated using browsing information local to the browser. One additional topic, chosen uniformly at random, is appended for a total of 6 topics associated with the user for that week/epoch.
Topics include fitness, travel, and news, with about 350 available initially. Topics are kept for three weeks before being automatically deleted, and Chrome will let users see and remove their topics at will – or disable the feature entirely. Google says topics are “thoughtfully curated” by humans and “will not include potentially sensitive categories, such as gender or race.”
When you visit a site that requests your topics, your browser will pick three – “one topic from each of the past three weeks” – to share with publication and advertising partners. Those third-parties will use that information to serve ads relevant to your interests/topics.
A developer trial of the Topics API is launching in Chrome by the end of Q1 2022. This will allow websites and the ads industry to test while topic deletion controls will be present. The Topics API’s effectiveness for ads compared to third-party cookies is not yet clear.
The final design of the user controls and the other various technical aspects of how Topics works will be decided based on your feedback and what we learn in the trial.
Overall, the Topics API seems more generalized than FLoC. Compared to cookies, Google wants to “make Topics easier to understand and manage for users.” More details are provided in this technical explainer.
The Topics API significantly reduces the amount of cross-site identifiable information. The coarseness of the topics makes each topic a very weak signal; different sites receiving different topics further dilutes its utility for fingerprinting.
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