GoKawiilOpenAI's ChatGPT ad system links your browsing on other sites to your account via '__obi' cookie
OpenAI runs an advertising collector at bzr.openai.com that sets a persistent, account-linked cookie called __obi on the openai.com domain. When companies that advertise on ChatGPT embed OpenAI's tracking code on their own websites, that cookie is transmitted back to OpenAI along with details of the page being viewed, including products searched, articles read and purchases made. A security researcher says they reproduced the mechanism on their own device and found it active across 936 advertiser pixels spanning 1,029 hostnames.
GoKawiil's interpretation of the reporting above, not reported fact.
This effectively turns ChatGPT into a cross-site tracking hub similar to Meta or Google's ad pixels, but tied directly to a user's identified AI chat account rather than an anonymous ad ID. Because the cookie persists for a year and is cryptographically bound to the account via a signed token, OpenAI can potentially build detailed profiles of users' off-platform browsing and shopping habits. It raises fresh questions about how AI companies handle consent and data linkage as they expand into advertising.
- OpenAI sets a year-long __obi cookie on openai.com tied to a user's ChatGPT account identity.
- Advertisers on ChatGPT install OpenAI's tracking code on their own sites, which reports browsing activity back using that cookie.
- Researcher verified the mechanism directly and found it deployed across nearly 1,000 advertiser hostnames.
Source: buchodi.com, 2026-09-20
Published there as: “ChatGPT now knows what you do on other websites via ad collector”
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