As a replacement for the FLoc targeting technology, Google has opted to use the Topics API

Users’ browser history is used to identify which topics to share with websites and advertisers in the new Privacy Sandbox concept.
Google announced on Tuesday that Topics, a new interest-based targeting idea, will take the place of Federated Learning of Cohorts (FLoC). Because it uses the user’s browser history to select topics of interest, the Subjects API eliminates the need for third-party servers.

Google aims to launch a developer trial of Topics in Chrome, which will feature user controls (more on that later) (more on that later). According to Google, the final version of the user controls and other technical features of Topics operates will be set by the experiment and feedback.

How Topics will function
“With Themes,” Google explained, “your browser picks several topics, such as ‘Fitness’ or ‘Travel,’ that represent your key interests for that week based on your browsing history.”

Subjects ask a user to select three topics they want to share with the site and its advertising partners when they visit a participating location (one from each preceding three weeks). The browser can be linked to up to five distinct themes. Subject selection is made entirely on the device itself, with no help from Google’s servers or another third party.
According to Chrome product director Ben Galbraith: “This is a starting point; we might see this going into the low thousands or staying in the hundreds [of themes]. This list might grow to include tens of thousands of topics, or it could remain in the hundreds for the time being.

A Google spokesperson clarified that the search engine does not examine an article’s language; instead, it looks at the site’s URL or subdomain.

Galbraith said that the Topics API “does not give nor receive a subject if a site does not participate,” Galbraith said. Neither the site nor its advertising partners are barred from using the Topics API.

Google has also described the Topics concept in technical terms

FLoC and Topics are separate concepts. One of the key distinctions between Google’s previous targeting strategy, FLoC, and the Topics API is that Topics does not group people into cohorts. Fingerprinting techniques may be used to distinguish a user’s browser from the thousands of others in the same cohort and produce an individual identifier for that browser, as noted by the Electronic Frontier Foundation (EFF).
This information is used to assign users to a cohort, and new cohorts are created every week based on the previous week’s browsing statistics using the FLoC browser. The Subjects API selects subjects based on the user’s browser history every week, but the topics are only preserved for three weeks.

FLoC employs a cohort ID to communicate with sites and marketers, whereas Themes selects three topics.
Controls and privacy protections are available for each topic. Chrome users will soon be able to see the topics to which they’ve been related, thanks to new features being developed by Google. Users will be able to remove or disable individual subjects. At this moment, there are no plans to allow people to add their topics.

In addition, Google says that the subjects are chosen to exclude sensitive categories like race or sexual orientation.
Only time will tell which browsers will be embraced. While developing the Topics API, Google hasn’t had an opportunity to test it with other browsers. It’s hardly expected that any of the other browsers will follow Chrome’s lead by adopting the FLoC successor this time around.

As Galbraith explained, “We’re providing the explanation, which is the first step in that process of discussing other browsers’ viewpoints on the Topics API.”

It is impossible to predict which browsers will be the most popular until the future has passed. Google’s Topics API is still in the early stages of development, so other browsers haven’t had a chance to test it. Because Chrome was the only browser to accept its predecessor, Firefox, Safari, Edge, and other browsers are unlikely to follow Chrome’s lead this time (FLoC).
Finally, according to Galbraith, this is the first step in responding to other browsers’ concerns about the Topics API. “We’re posting the explanation.”