Research suggests OpenAI’s ad pixel may link ChatGPT ad activity to off-site behavior using the __obi cookie.
OpenAI’s move into advertising appears to be expanding beyond what happens inside ChatGPT.
An independent researcher who goes by Buchodi found that a cookie associated with ChatGPT can reappear when the same browser visits websites using OpenAI’s advertising pixel. The finding suggests OpenAI may be testing a way to connect ChatGPT ad interactions with later activity on participating advertiser sites.
The system centers on a cookie called __obi. OpenAI’s cookie policy lists it as an analytics cookie with a one-year duration, while OpenAI’s advertising documentation confirms that advertisers can use a pixel and Conversions API to measure actions after someone engages with a ChatGPT ad.
Buchodi’s research found that the same identifier could be sent back to OpenAI from participating advertiser sites, along with page and conversion data. The research did not confirm whether OpenAI links that activity to a named ChatGPT account on the server side.
For marketers, the appeal is clear. Better conversion measurement could make ChatGPT Ads easier to evaluate, especially compared with early ad channels that offer limited attribution data.
The privacy question is harder. ChatGPT users often share more personal context than they would with a search engine or social platform, so connecting chatbot activity to off-platform behavior could create sharper concerns around consent and disclosure.
There is also a classification issue. If __obi is treated as an analytics cookie, users may not expect it to support advertising attribution across other sites.
For advertisers, the practical takeaway is caution. Improved measurement is useful, but brands testing ChatGPT Ads should understand exactly what the pixel collects, how consent is handled and whether their privacy disclosures clearly explain the tracking involved.
As AI platforms move deeper into advertising, attribution will not be only a performance question. It will also become a trust question.
