The Topics API is a Privacy Sandbox mechanism designed to preserve privacy while allowing for interest-based advertising (IBA). The API is available for both web and android.
What is the Topics API?
Interest-based advertising is a key concept in the Topics API. It is a form of personalized advertising in which an ad is selected for a user based on their interests, inferred from the user's activity: the sites they've recently visited on the web, or the apps they used on Android. This is different from contextual advertising, which aims to match ads to the content the user is viewing.
Interest-based advertising can help both advertisers (parties that want to advertise their products or services) and publishers (parties that use ads to help monetize their content):
- IBA can help advertisers reach potential customers.
- IBA can supplement contextual information to help publishers use advertising to fund their platform.
- IBA helps to monetize apps and websites through relevant ads, even if their content is non-profit or otherwise difficult to commercialize.
The Topics API provides a new form of interest-based advertising using topics. A topic is a human-readable category representing a user's interest (e.g., "Fitness" or "Technology") that is assigned to a user based on their recent activity. These topics can supplement contextual information to help select appropriate advertisements.
How it works
To infer user interests, the Topics API observes on-device activity like app usage or website visits. These interests are represented as coarse-grained "topics". Topics are shared with advertisers to help them select and serve more relevant ads.
The Topics API offers a privacy-preserving alternative. It enables the browser or app to observe and record topics that seem to interest the user, based on their activity. This information is stored locally on the user's device. The API then allows authorized parties (like ad tech platforms) access to these general interest topics, without revealing specific details about the user's browsing or app usage history.
How Topics API reduces fingerprinting
The Topics API provides multiple mechanisms to help ensure that it is difficult to re-identify significant numbers of users across sites and apps using the Topics API alone:
- Because the Topics taxonomy provides coarsely grained topics, each topic is expected to have large numbers of users. In fact, there is a minimum number of users per topic, because 5% of the time the returned topic is random.
- Topics are returned at random from the user's top five.
- If a user frequently visits the same site or app (every week, for example) a third party can learn one new topic per week, at most.
- Different callers will receive different topics for the same user in the same epoch. There is only a one-in-five chance that the topic returned for a user on one site or app matches the topic returned for them on another. This makes it more difficult to determine if they're the same user.
- Topics are updated for a user once each week, which limits the rate at which information can be shared. In other words, the API helps mitigate against fingerprinting by not providing topic updates too frequently.
- A topic will only be returned for an API caller that previously observed the same topic for the same user recently. This approach helps limit the potential for entities to learn about (or share) information about user interests they have not observed firsthand.
- The inference of user interest is processed on the device: The user's information about exactly what sites or apps user accesses does not leave the device, and privacy is protected. This model is in contrast to the current commonly-used model of having a user's cross-site or cross-app data being sent and processed off the device, on ad tech servers. Certain types of processing will continue to remain on ad tech servers, such as using the signals provided by the Topics API in personalization and optimization models for ad selection.
How the API addressed concerns with FLoC
The origin trial of FLoC in 2021 received a wide range of feedback from ad tech and web ecosystem contributors. In particular, there were concerns that FLoC cohorts could be used as a fingerprinting surface to identify users, or could reveal a user's association with a sensitive category. There were also calls to make FLoC more transparent and understandable to users.
The Topics API has been designed with this feedback in mind. It aims to explore other ways to support interest-based advertising, with improved transparency, stronger privacy assurances and a different approach for sensitive categories.
User and developer controls, transparency, and opting out
Users should be able to understand the purpose of the Topics API, recognize what is being said about them, know when the API is in use, and be provided with controls to enable or disable it.
The API's human-readable taxonomy enables users to learn about and control the topics that may be suggested for them. Users can remove topics they specifically don't want the Topics API to share with advertisers or publishers, and there can be controls to inform the user about the API and show how to enable or disable it. In addition to the user's ability to opt out, you can opt out of Topics for your site or app.
Read the specific implementation guide for Web or Android to find out how users and developers can opt out of Topics.
To sum up, the Topics API offers a win-win solution: it safeguards user privacy while enabling sustainable revenue streams for content creators and delivering more relevant advertising experiences, making it a privacy-oriented alternative of current ad targeting technologies.