Interest groups are a fundamental concept in the Protected Audience API. They allow advertisers to target groups of users with shared interests (corresponding to a remarketing list), without relying on individual tracking or cross-site identifiers. Think of it as a way to categorize users based on their online behavior, such as “people interested in running shoes” or “people who have recently visited a travel website.” You can learn more about interest groups here.
NOTE: If there is a collaborative use of interest groups that you don't see supported yet, file a GitHub issue so Chrome can learn more.
How do interest groups protect privacy?
Interest group membership is stored by the browser, on the user’s device, and is not shared with the browser vendor or anyone else.
Sites will need to set a permission policy to allow users on their site to be added to interest groups (for example, an advertiser adding a user to a remarketing list). Refer to the developer documentation for more information.
Currently, an advertiser can associate a given user with up to 2000 interest groups, although this limit is not final and may change depending on feedback.
Protected Audience interest groups expire after 30 days, unless the API caller specifies a shorter expiry or the user deletes interest groups or disables the API.