OpenAI's ChatGPT cookie may track users across websites for ad measurement
A researcher found that a cookie named __obi set by ChatGPT can persist for up to a year and reappear on sites using OpenAI's ad pixel, potentially linking ad interactions to later activity. This could improve ad measurement but raises privacy concerns because ChatGPT users share more personal data. OpenAI classifies the cookie as analytics, but the consent language may need scrutiny.
The __obi cookie functions as a persistent identifier that OpenAI can set within a user's browser during ChatGPT sessions, with a lifespan of up to one year. When that same browser later encounters websites equipped with OpenAI's advertising pixel, the identifier is transmitted alongside page views and conversion signals, creating a bridge between chatbot interactions and off-platform browsing behavior. The researcher Buchodi did not confirm whether OpenAI's servers ultimately link this data to specific named accounts, leaving the full scope of identity resolution unverified.
OpenAI currently categorizes __obi under its analytics consent tier rather than marketing cookies. This classification means the cookie may activate even when users explicitly decline marketing-related tracking, provided they accept analytics tracking. The distinction is significant because typical users interpret "analytics" as internal site measurement, not cross-site advertising attribution, raising questions about whether the current consent language accurately reflects the cookie's reported functionality.
This tracking mechanism could affect ChatGPT users who assume their conversations remain contained within the platform, as their browsing activity on advertiser sites may now inform ad measurement tied to their chatbot usage. Because ChatGPT users often share sensitive personal and professional information, the potential linkage between that data and off-site behavior may heighten privacy concerns and erode trust in AI platforms. Regulators and consent frameworks could face pressure to clarify whether "analytics" labels adequately cover cross-site advertising purposes, potentially reshaping how AI companies design tracking disclosures.