Guide · Advertising
Google Topics API: what it means for ad targeting
Google Topics API is a browser feature that shares a few broad interests with sites so they can show relevant ads without tracking people across the web. Google announced it on 25 January 2022. This guide explains how it works and what marketers can still target.
What the Topics API is
On 25 January 2022, Google announced Topics, a new Privacy Sandbox proposal for interest-based advertising. It replaces the earlier FLoC idea. Google says it was shaped by what it learned from the FLoC trials and by feedback from the community.
Interest-based advertising means an ad is picked from interests drawn from sites a person visited in the past. That is different from contextual advertising, which looks only at the page a person is on right now. Topics is a way to keep the first kind working as browsers move away from third party cookies.
It is a proposal, not a finished product. Google says a developer trial in Chrome will start soon, and that the final design will depend on feedback and on what the trial shows.
Sources: Google, Get to know the new Topics API for Privacy Sandbox; Topics API explainer on GitHub
How topics are chosen
The browser does the work. It looks at the sites a person visits and sorts them into a short list of broad topics, such as "Fitness" or "Travel & Transportation." Google says this happens on the device, with no outside servers involved, Google servers included.
The explainer gives the details. Each week the browser works out the person's top five topics. It adds one random topic, so six are kept. When a site asks for topics, it gets up to three, one for each of the last three weeks. A small share of answers, about 5%, is a random topic on purpose, to add noise and protect privacy.
The browser decides a site's topic from its hostname, not from the full page address or the page text. So a site on its own subdomain, such as tennis.example.com, can fit a tennis topic, while a page at example.com/tennis only takes the topics of the main site. All of this is still open to change.
Sources: Google, Get to know the new Topics API for Privacy Sandbox; Topics API explainer on GitHub
What marketers can see
The topic list is a public taxonomy. The first draft has about 350 topics, and Google says it will try to leave out sensitive ones, such as those tied to gender or race. The plan is for an outside party to own the list over time.
Each topic comes back as a number, with a taxonomy version and a classifier version. Ad tech firms can look the number up in the public list. The list is coarse. It tells you someone follows travel news. It does not tell you which sites they visited.
There is a second limit. A company only learns a topic if it has already seen that person on a site about that topic in the past three weeks. So the API does not hand a company more than third party cookies would have shown it.
Sources: Topics API explainer on GitHub
What people get to control
Google says Topics is meant to be easier to see and manage than a cookie. Topics are kept for three weeks, and then old ones are deleted. In Chrome, Google is building controls that let a person see their topics, remove any they dislike, or turn the feature off.
If a person turns it off, the pages they visit do not count toward their weekly topics. The explainer also says a page can opt out with a response header. For advertisers this means topic data will be missing for some visitors, and plans should allow for that.
Sources: Google, Get to know the new Topics API for Privacy Sandbox; Topics API explainer on GitHub
What you can still target
Topics is one signal, not a full replacement for cookies. It gives a few broad interests per visitor. It will not follow a person from site to site, and it will not support the detailed audience lists many teams use today.
Here is a sensible way to prepare while the trial is pending:
- Lean on contextual targeting, which uses the page itself and needs no personal data.
- Build first party data: email sign ups, account data and purchase history that people hand over with consent.
- Keep your campaign tests flexible, so you can compare topic based buying with other methods once it is available.
- Watch the trial. Google says details can change, so avoid building plans on numbers that are still drafts.
Nothing here is live yet. Treat it as a proposal to learn, not a setting to switch on.
Sources: Google, Get to know the new Topics API for Privacy Sandbox; Topics API explainer on GitHub
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