Google has announced it won't be replacing cookies with FLoC, the web browser tracking protocol it created to help deliver users personalized ad content — and had been maligned by privacy advocates — after all. Instead, the company will attempt to fulfill the same mission without as much intrusion with a new API dubbed Topics.

The proposed API comes out of the Privacy Sandbox, a web standards working group spearheaded by the Google Chrome team. A rough draft is available for inspection on GitHub with specific details subject to change.

In short, an ad service that wants to show content to a website visitor calls for the Topics API, based at the browser level, and will receive up to three associated interests. An interest comes from a pool of five top topics from each of the past three weeks plus a completely random topic to add in statistical noise. The API may filter out certain topics to give out based on certain determinations such as the caller or visitor not having used the API for a certain period — visitors can disable the API in the settings or by using Incognito Mode — or simply not allowing certain sites to see that a visitor has seen certain topics.

Users' topical histories are generated by measuring visits to websites via a "classifier" AI model that associates website hostnames with a determined topic or topics — the API won't log topics from a website that doesn't call on it and may not do so if the classifier fails. The initial list of topics tallies more than 300, but Google may adopt hundreds more based on industry standards. Users can also remove certain topics from their browsing history. Google is seeking advice to exclude sensitive topics from the API.

Google says Topics give visitors an edge on privacy with the layers of randomization, local data processing, and the filtering the API does while still giving ad providers enough of an idea of how to target and personalize content. Most importantly, ad providers won't know which sites users have browsed.

Developers will be able to try the API in Chrome in the near future.

With this new proposal, Google has canned its original replacement for third-party cookies, Federated Learning of Cohorts. It would've grouped web users with similar browsing behaviors into flocks and let ad providers track their general interests to serve personalized ads, shuffling them every week. Web developers, browser publishers, and even the European Union have laid plenty of criticism against FLoC where ad providers could potentially identify users through other means like IP address and log their cohort participation over time to open up more insight than the current system of cookies might have otherwise given. It may also have opened up ad providers to some revelatory loopholes as well. As of July last year, the company had rolled back its deployment of FLoC on Chrome from the fall of last year all the way to 2023. Other browsers promised not to adopt the standard.

In November, Google pledged to the UK's Competition and Markets Authority that it wouldn't disable third-party cookies on Chrome without extensive, supervised trial of a replacement and that it would carry out development under the CMA's conditions globally. The Privacy Sandbox was the company's way to handle that and Topics seems to be a fruit of its commitment. The road to approval looks to be lengthy and shrouded in uncertainty, much as the pathway up was.