The Topics API determines a user's interests based on their browsing history, but it does so in a way that protects their privacy. Here's how topics are assigned to a user:
- Device and profile specific: Topics are specific to a device and a Chrome user profile. They are not shared across devices, even for the same profile. So, if a user has multiple devices and tends to consume different kinds of content on each device, the topics could be different.
- Based on API usage: Only visits to pages that include the Topics API will be included in the calculation of a user's topics.
- Across all participating sites: The topic that is assigned to a person for that time period is based on their activity across all participating sites, while taking commercial value and frequency into account.
Learn more in the developer documentation.