Google’s Decision is In: FLoC Will Replace Third-Party Cookies

Tim Cross 25 January, 2021 

Google today has effectively committed to Federated Learning of Cohorts (FLoC), one of the tools developed in its ‘privacy sandbox’, as a replacement for third-party cookies within its Chrome Browser.

Google says FLoC, an API which enables ad targeting based on users’ general interests, has proven to be 95 percent as effective as third-party cookies in terms of conversions per dollar spent. Having proven FLoC’s viability in private, Google says it will roll out FLoC for wider testing in March.

It isn’t yet clear how granular the cohorts will be, so for example we don’t yet know whether cohorts will be ‘classical music lovers’ or ‘in-market trombone buyers’. This is expected to be clarified in March.

For those paying attention, there were already signs that Google was betting on FLoC. As Zach Edwards, founder of analytics and optimisation firm Victory Medium, told VideoWeek a few weeks ago, Google has already written thousands of FLoC references into the Chromium code base.

But now with Google touting FLoC’s effectiveness, while also confirming that it will use privacy sandbox tools to power its own web advertising products once third-party cookies are no longer supported, it’s clear that FLoC will be a major component of digital advertising in the coming years.

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Just one piece of the puzzle

FLoC is not a wholesale replacement for third-party cookies. The API specifically enables targeting based on users’ general interests. Things like measurement and fraud prevention, which third-party cookies are used for, are not handled by FLoC.

And retargeting isn’t possible through FLoC either. Separate proposals, like TURTLEDOVE, SPARROW, and the newly announced FLEDGE, have been developed to tackle this specific use case.

But FLoC is designed to enable targeting based on users’ general interests, which it does by clustering large groups of people with similar interests (called ‘cohorts’).

The central idea behind FLoC is that the browser feeds data on which websites a user visits into a machine learning algorithm, which operates within the browser. This algorithm decides which cohort that user should belong to, matching the user to a large group of other users with similar interests.

So for example, the browser might see that a particular user visits a lot of websites about football, fashion, and baking. This user might then be placed into a cohort with other football, fashion, and baking enthusiasts.

Advertisers are then able to target these cohorts, based on the interests of the users inside those cohorts, enabling interest-based targeting.

But individual users’ browsing data doesn’t leave their browser. So in the example above, the browser wouldn’t declare which football, fashion and baking websites the user had visited. It would only broadcast a ‘cohort ID’, declaring which cohort the user belongs to.

And Google says that if these cohorts are large enough, it won’t be possible to track individual users, meaning privacy is preserved.

That’s not to say that there are no privacy risks with the FLoC API. One, acknowledged by Google, is that the machine learning algorithm could unintentionally build cohorts which reveal sensitive categories like race, sexuality, or personal hardships. Google says that in tests so far. These cohorts have been blocked, or the algorithm has been reconfigured to avoid them being produced.

Some are also sceptical about whether the cohort approach really maintains privacy. Mathieu Roche, CEO of identity specialist ID5, told VAN that grouping users together might make it harder for individual users to understand how their data is being used, and who is targeting them.

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One year on the clock

Regardless of any issues with FLoC, today’s announcement means that the wider industry will soon be able to test FLoC’s strengths and weaknesses for themselves. Following the release of FLoC cohorts for public testing in March, Google says it will begin testing user controls for privacy sandbox tools in April.

There was no hint in today’s announcement that Google’s January 2021 deadline to end support for third-party cookies will be extended. That means that for the time being, the industry should assume it has one year to adapt to FLoC.

And other sandbox tools to handle measurement, retargeting, and fraud prevention, will also have to be polished up ready for the deadline. While Google is confident in its belief that FLoC is a viable replacement for third-party cookies, these other tools have not yet been proven to work to the same extent.

Nonetheless, Google says it is “more confident than ever that the Privacy Sandbox is the best path forward to improve privacy for web users while ensuring publishers can earn what they need to fund great content and advertisers can reach the right people for their products”.

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About the Author:

Tim Cross is Assistant Editor at VideoWeek.
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