FloC: all you need to know about replacing Google Chrome advertising cookies

A few weeks ago, Google announced that it would stop supporting third-party cookies in the Chrome browser as early as 2022. This move will obviously change the way businesses track their users on the Internet. So, will the Mountain View firm stop tracking its users? Of course not: Google will replace third-party cookies with FLoC, or Federated Learning of Cohorts. We tell you everything.

Federated Learning of Cohorts
FLoC © Google

With the decline of cookies, in part due to many browsers blocking third-party cookies by default, Google wants to offer another way to track user data for targeted advertising. This is where comes in FLoC, one of the proposals of the community and open source initiative of Google named Privacy Sandbox, which aims to help publishers better respect user privacy.

Born in the premises of Google Ads, Federated Learning of Cohorts (Federated Cohort Learning) or FLoC is therefore an advertising tracking system on the Internet offered by Google. It is placed as an alternative to cookies. Google has launched tests of the functionality on some Chrome users in April 2021 and plans to permanently deploy its new system by the end of the year. So what is it and what to expect?

What is FLoC?

At a time when the constant tracking of Internet users encourages them to no longer accept the collection of their data, the mastodons of the Web are looking for a new model, a new strategy. While Apple already offers tools to combat tracking with App Tracking Transparency, many other players are looking for another way to track users.

FLoC is Google’s alternative to third-party cookies, based on machine learning. Meaning Federated Learning of Cohorts, or federated learning of cohorts in French, this will – in theory – allow any Internet browser to anonymously study how users browse the Web.

Google Chrome users will be grouped into “cohorts”: a group of individuals who share the same interests. The goal being to Deliver targeted advertising to them, but collectively, rather than individually. Advertisers will then be able to see the behaviors shared by people in the same cohort, but without being able to identify them individually, because each person’s browser receives an anonymized identifier. These anonymized identifiers (called Cohort ID, sometimes renamed FLoC ID) will be recalculated every week, providing each time a new summary of online user behavior.

© Google

For example, a cohort might be made up of thousands of people who have recently visited gardening and overseas travel websites; another cohort may be a group of people who have recently visited cooking and hiking sites. Each individual’s browser uses FLoC technology to determine which cohort most closely matches their recent web browsing history, then advertisers collectively serve ads to each cohort.

To summarize, Google Chrome generates “cohorts” of users with similar browsing histories. Then, advertisers serve ads to these cohorts, more without recognizing the individuals who appear there. Thus, cohorts are not based on who the individuals are, but rather on their collective interests, with the goal that advertisers can serve relevant ads. Google says that since there will be thousands of people in each cohort, no one could be selected from the group and associated with their unique browsing data.

What do Google and advertisers think?

In fact, FLoC already offers a conversion level per dollar of around 95% compared to traditional cookie tracking. This figure appeals to advertisers and shows that it is an effective solution for generating audiences targeted by area of ​​interest. Most of the major groups, such as Amazon or Microsoft, have so far remained silent on this subject.

What do the detractors think?

While being placed in a cohort theoretically makes it possible not to be individually identified, privacy-focused browsers DuckDuckGo, Brave, and Vivaldi all have warned users about FLoC. All said they were going to block it on their side.

Indeed, the developers of DuckDuckGo have pointed out that Google has not left a choice to Chrome users. FLoC will not be an option: it will be a requirement to be able to use the Google browser. DuckDuckGo added that in response to automatic activation of FLoC by Google, blocking trackers on their own Chrome extension has been reviewed and fixed in order to block all FLoC interactions on websites.

See also: Google Chrome: how to delete browsing history and cookies

Brave Software teams also said they will block FloC and have it already disabled on the Nightly version of Brave, on PC and Android. ” The worst aspect of FLoC is that it invades users’ privacy, on the pretext that it is privacy friendly. ”Say the founders of the browser in a blog post. The same goes for WordPress, whose infrastructure for 41% of websites is based on this CMS. The tool already offers to disable FLoC by default.

Thus, FLoC can “ exacerbating many of the worst privacy concerns associated with behavioral advertising, including discrimination and predatory targeting The Electronic Frontier Foundation said in a statement. Despite this massive outcry, Google has been testing FLoC on Google Chrome since the second quarter of 2021 and should put it in place definitively by 2022.

How do I know if I am affected by FLoC? How to withdraw and how not to be touched?

To find out if you have been assigned a Cohort ID, go here. If so, the only way to opt out of FLoC in Chrome is to disable third-party cookies from the browser. This may reset your preferences on some sites and interrupt features such as single sign-on.

The other solution to not be affected by FLoC immediately is to use another browser like Firefox, as well as Chromium-based browsers like Microsoft Edge or Brave, which currently do not have FLoC active. Safari neither, if you are using macOS.

And if you are a website owner, your site will automatically be included in FLoC calculations if it accesses the FLoC API or if Chrome detects that it is serving ads. You can disable this calculation by sending the following HTTP response header:

Find all the official information on FLoC at this address.


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