The Topics API is Google’s latest replacement for the third-party cookie and aims to create a privacy-focused, interest-based advertising model. But what is Topics? How does it work? And why was it created? Here, we answer these questions and many more

As one of the world’s biggest players in digital advertising, all eyes are on Google and what its plans are for a successor to the third-party cookie. The outcome will play a huge part in reshaping a multi-billion-dollar industry with an uncertain future.

While Google’s initial alternative was the Federated Learning of Cohorts (FLoC), the tech giant has since ceased its development in favor of an advertising system called Topics.

In this article, we examine what the Topics API is, how it works, and why it was created. We’ll also take a closer look at FLoC, exploring the criticism it received and the reasons why it was abandoned.

What is Google Topics?

Topics is Google’s proposed privacy-friendly replacement for third-party cookies. It’s a browser-based system that assigns a user a set of interests according to the websites they have visited.

Once these interests have been allocated, the Topics API shares them with participating websites and ad tech companies to power personalized digital advertising.

With all tracking happening on-device, data only being stored for a maximum of three weeks, and no information shared with any external servers (including its own), Google is presenting the Topics API as a potential compromise between ad personalization and user privacy that will shape the future of the post-cookie industry. The company is, however, careful to note in its explainer that the technology is still in the early stages of testing.

How does Google Topics work?

If your browser supports Topics, each week it will automatically assign you a number of categories (or ‘topics’) based on the websites you’ve visited.

Examples of these categories could be Travel & Transportation or Books & Literature. They will be selected from an initial list of 350 that has been curated by Google, a number that is likely to increase as the product evolves, and will not include anything sensitive such as gender or race.

Once Topics has created three of these weekly batches, it will randomly select one category from each batch to share with a participating website that you visit.

The participating website (or the ad tech company that manages its inventory) then uses this information to serve you targeted digital ads while you’re there.

Google has stated that Topics will only ever hold data from a maximum three-week period. So, when week four begins, all categories from week one are deleted, and when week five begins all categories from week two are deleted, and so on.

The aim is to create a form of targeting that keeps the user’s personal data completely anonymous, which Google describes as interest-based advertising.

Can you opt out of Google Topics?

Yes, websites and users can both opt out of Google’s Topics API.

This is because Topics requires the participation of four parties to work: the browser, the user, the website being visited, and the website serving the advertising.

With Topics still in the early testing phase, Chrome is currently the only browser that’s set to support it. It remains to be seen how it might look elsewhere, or indeed if it will even enjoy wider adoption. 

However, Google has confirmed in an article on its Chrome Developers site that Chrome users will not only be able to view the categories they have been assigned, but they will also be able to remove individual categories and even switch off Topics completely if they wish. It will also be possible to remove all stored categories by clearing browsing history, and to disable Topics by entering Chrome’s Incognito mode.

When it comes to websites, weekly categories will only be generated from visits to domains that also use the Topics API. Equally, only websites that use the API can retrieve these categories.

Additionally, if a website specifically wants to opt out, it can forbid topic calculation using the following Permissions Policy header:

Permissions-Policy: browsing-topics=()

When will Google Topics be available?

There is currently no set date for the implementation of Topics. Google has stated that it will be performing extensive testing globally before the technology is adopted.

The results of this testing and the feedback received by the web community will dictate the timeline for implementation.

Why was Google Topics created?

With the third-party cookie soon to be phased out completely, the digital advertising industry is looking for new ways to target audiences without using personal data.

As the biggest player in the industry, it was certainly within Google’s interests to fill the hole left by behavioral targeting that was achieved using third-party data. Its answer was something called the Federated Learning of Cohorts (FLoC).

FLoC was, however, met with widespread criticism from privacy advocates and has subsequently been scrapped. Topics was created as a replacement for FLoC, which addresses these privacy concerns.

What was the Federated Learning of Cohorts (FLoC)?

FLoC was Google’s first attempt at a replacement for the third-party cookie. It worked in a similar way to Topics in that it used a browser-based tracking system to monitor a user’s online behavior. However, this information was then used to allocate each user to a specific group with similar interests, otherwise known as a ‘cohort’.

Every user in a said cohort was given the same cohort ID, which advertisers could then use for targeting based on their recent activity.

The idea was that a user’s identity and specific behavior would be lost among thousands of individuals, maintaining anonymity and ultimately online privacy.

Why did Google abandon FLoC?

Following its release, FLoC endured a barrage of criticism from many of the industry’s biggest players.

Blogs from Vivaldi, Brave, GitHub, DuckDuckGo, and Electronic Frontier Foundation (EFF) all made their opposition clear. Additionally, no other browser adopted the technology, while companies such as Twitter and Amazon removed it from their platforms.

The main concern was that FLoC facilitated fingerprinting – a practice in which a third party secretly gathers small pieces of data about a user’s device in order to build up a unique profile for that user, which can then be used to track them online.

Examples of this data could be device and app preferences, language settings, or location. Such small pieces of information might seem relatively useless individually, but when enough of these are combined, they can create astonishingly accurate profiles.

Unlike third-party cookies, fingerprinting data is not stored on the user’s device and therefore cannot be easily deleted.

The argument against FLoC was that, while trackers would ordinarily have to begin profiling an individual from a pool of millions, by placing them in a cohort based on their browsing activity, FLoC would narrow that figure down to just a few thousand, effectively doing a large amount of the initial legwork.

Ironically, this means that in its attempt to protect a user’s privacy, FLoC did exactly the opposite.

How has Google Topics addressed the problems with FLoC and fingerprinting?

Topics attempts to address the fingerprinting issues associated with FLoC in a number of ways.

First, because Topics randomly chooses just one category from each weekly batch to share with a website, the combination of categories will likely differ from site to site, protecting anonymity.

Second, categories are only stored for a maximum of three weeks and are renewed on a weekly basis. This ensures there’s only ever information on a user’s most recent history.

Third, 5% of the time, Topics includes a dummy category that has been selected from the taxonomy completely at random. This makes it harder for trackers to identify behavioral patterns.

Additionally, Topics addresses concerns surrounding user transparency. Whereas FLoC used a cohort ID made up of indistinguishable code, Topics uses categories taken from a human-curated list. This ensures users can easily see and understand exactly which categories they have been assigned. 

Furthermore, Topics also allows users to remove categories as they wish, and even opt out of the technology altogether, keeping them in full control.

The future for Google Topics

With Topics yet to be released for global testing, it remains to be seen exactly how well it will be received by the industry.

However, with this new solution still fundamentally relying on the gathering and sharing of user data – albeit significantly less of it – it’s likely that companies behind privacy-focused browsers such as Firefox, Brave, and Vivaldi will reject it in the same way they rejected FLoC.

Furthermore, Apple’s renewed focus on user privacy with the release of iOS 14.5 – and the success it has seen – could mean Safari will also follow suit.

This in itself creates possibly the biggest challenge for Topics: widespread adoption. The Topics API is currently only supported by Chrome, and while it will be easy for any browser to adopt the technology, there are no guarantees they actually will.

With a 65% share, Chrome very much dominates the worldwide browser market, but that still leaves 35% up for grabs. In the context of a global digital advertising industry, which was worth an estimated $491bn last year, that’s a portion worth fighting for.

With Alphabet (Google’s parent company) relying on advertising for over 80% of its profits, we could see it explore and develop other forms of targeting such as contextual advertising to maintain its dominance in the digital advertising industry.

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