OpenAI's ad collector links user activity on external sites to ChatGPT accounts

OpenAI's ad collector sets a cookie called __obi, which is tied to a user's ChatGPT account and is sent to OpenAI when users visit other websites that have OpenAI's advertising code installed.

The __obi cookie allows OpenAI to connect user activities, such as product searches and reading habits, on external sites to their ChatGPT accounts. Advertisers using OpenAI's code can collect data about user interactions, including personal information like email and location, which is sometimes hashed before transmission.

The mechanism operates by generating a unique identifier for each user session, which is then stored as a cookie on OpenAI's domain. This cookie is sent back to OpenAI when users interact with advertiser sites, allowing for detailed tracking of user behavior.

OpenAI classifies __obi as an analytics cookie, which is intended to help understand service performance. Users can grant or refuse consent for analytics and marketing separately, but the implications of this tracking on user privacy are significant, especially given the sensitive nature of interactions with AI chat products.

The tracking mechanism is not functional on iOS browsers due to restrictions on third-party cookies, and it has been observed primarily on Chrome for Android. OpenAI has not provided clear answers regarding the classification of the __obi cookie or its implications for user consent.