Researcher finds OpenAI using third-party cookie to track ChatGPT users across advertiser sites

MARTECH reports on findings by researcher Buchodi showing that OpenAI places a cookie called __obi in browsers during ChatGPT use, which can persist for up to a year and reappear when users visit sites running OpenAI's advertising pixel. The identifier can travel between ChatGPT and advertiser sites back to OpenAI, enabling conversion tracking without necessarily linking activity to named user accounts. However, OpenAI classifies the cookie as "analytics" rather than "marketing," raising questions about whether users granting analytics consent understood it would enable cross-site ad attribution—and whether the practice complies with varying data-protection regulations.