Federated Learning of Cohorts (FLoC)

Federated Learning of Cohorts (FLoC) is a new way for advertisers and sites to show relevant ads without tracking individuals across the web. FLoC was developed with the idea to protect individuals' privacy by placing them in a large crowd — a cohort — of thousands of people with similar recent browsing activity without any of them being individually identified.
Federated Learning of Cohorts (FLoC) presentation video

How it works

The Federated Learning of Cohorts (FLoC) uses an open source technology that looks for clusters of similar information. In this case, it’s used to create cohorts of people based on their web browsing activity. For example, one cohort can be thousands of people who have recently visited websites about gardening and travel overseas; another cohort can be a group of people who have recently visited sites about art supplies, cooking, and hiking. Your browser uses the FLoC technology to determine which cohort corresponds most closely to your recent web browsing history.

Privacy improvements

You’re part of a crowd. FLoC keeps you among a large group of people with similar browsing history. This group isn’t based on who the individuals are, but rather on their collective interests so advertisers can still show relevant ads.
Your personal browsing history doesn’t leave your browser or your device, and it’s not shared with anyone, including advertisers. This means you can continue to see relevant ads and content without needing to be tracked across the web.

Frequently Asked Questions

Will I be in multiple FLoC cohorts at once?

No. Your browser will only place you in one cohort at a time, but any cohort might capture your interest in multiple topics, for example both gardening and travel.

If my interests change, do I stay in the same FLoC cohort?

No. Cohorts are dynamic and they will update every seven days. As your interests—and browsing behavior—change, so does your FLoC cohort.

Does Chrome share my browsing history with websites?

No. Chrome has designed FLoC as a way for websites to provide more relevant advertising without having access to your browsing history.

Will my FLoC cohort be based on sensitive categories, like race, religion, or sexuality?

No. Chrome won’t allow you to be placed in groups that are deemed sensitive. Before a cohort becomes active, Chrome analyzes it to see if the cohort is visiting pages with sensitive topics at a high rate. If so, the cohort is dropped before it’s ever used, and without learning which sensitive topics. Sites will also have the ability to opt out of FLoC if they choose to, so the visits to that site will not be considered by your browser when determining your cohort.

When will FLoC be rolled out?

The technology is still in the early stages. The results of the trials and feedback from the web community will inform the timeline.

Will Google Ads have any unfair advantage once FLoC is implemented in Google Chrome?

No. Google Ads will connect to the technology in the same way as other advertising platforms, publishers or advertisers. FLoC and other Privacy Sandbox innovations are open source and free to use so other members of the web community are invited to contribute and adopt them.

Where can I learn more?

The “What is Federated Learning of Cohorts” article on web.dev is a good start.