WHAT IS DOCUMENTED
● What it is: a browser SDK for measuring website events attributable to ads shown in ChatGPT.
● Where it talks to: script from bzrcdn.openai.com, events to bzr.openai.com.
● What it records: conversion events, optional hashed email, phone, name and external IDs, country, city, region and postal code, page URL and timestamps.
● How you are identified: an oppref value from the landing page URL, and a randomly generated __obref cookie that lasts 365 days.
Start with what is not controversial
This is not a leak. OpenAI publishes the specification on its developer site, the way Meta and Google publish theirs. An advertising business needs conversion measurement, and every advertising business builds this. Discovering that it exists is not the story.
Identifiers are hashed with SHA-256 in the browser before transmission, and the docs state that raw values stay local. Site owners can require consent before the pixel fires, restrict it with a content security policy, and flag events to be excluded from personalisation.
Now the part worth reading carefully
| Field |
Collected |
| Conversion events | Purchases, registrations, leads |
| Hashed identifiers | Email, phone, name, external IDs — optional |
| Location | Country, city, region, postal code |
| Page context | Source URL, timestamps |
| Persistence | __obref cookie, 365 days |
Hashing an email address is not the same as not collecting it. A SHA-256 of an email is a stable identifier for that person everywhere the same email appears, which is what makes cross-site matching work. That is the point of the feature, and it is a reasonable thing for advertisers to want — but describing it as privacy-preserving does more work than the word usually carries.
WHAT IS BEING REPORTED THAT WE CANNOT CONFIRM
Several outlets are reporting that the pixel binds a visitor's browsing to their logged-in ChatGPT account through a JWT-carrying cookie, based on reverse-engineering rather than documentation.
OpenAI's published specification describes oppref and __obref, not a JWT, and describes hashed identifiers rather than account binding. We are not repeating the stronger claim as fact. It may be correct and the documentation may be incomplete. It is not confirmed, and the difference between those two situations matters a great deal here.
Why this lands now
Three days ago we wrote that the hard question about ads in assistants is not labelling — it is whether the unsponsored answer changes because sponsorship exists.
The pixel is the other half of that. An advertising business needs measurement, measurement needs identity, and identity is what makes a recommendation engine worth paying for. None of the individual steps are sinister. The destination is an assistant that knows who you are across the web and also tells you which product to buy.
What you can actually do
- If you run a website: you decide whether this fires. Consent gating and a content security policy are both supported, and adding a pixel because a platform suggested it is how sites end up leaking more than they meant to.
- If you use ChatGPT: the cookie is first-party to the sites that install it, so ordinary cookie controls and tracker blocking apply. Check your OpenAI account privacy settings too.
- If you are in the EU or UK: hashed identifiers are still personal data under GDPR. Consent obligations sit with the site operator, not with OpenAI.
- If you want an assistant with no advertising at all: that is still a short list, and we keep it current.
Sources
FAQ
Does ChatGPT track me across other websites?
OpenAI's measurement pixel runs on websites that choose to install it and reports conversion events back to OpenAI. Its documentation describes hashed identifiers and a first-party cookie rather than account-level linking. Stronger claims are circulating and are not confirmed by the published specification.
What is the __obref cookie?
A randomly generated browser reference stored for 365 days, used to attribute a conversion to an ad interaction.
Is hashed data anonymous?
No. A hash of an email address is a stable identifier for that address wherever it appears, which is precisely what enables matching across sites.
Can I stop it?
It runs on sites that install it, so normal cookie controls and tracker blocking apply. Site owners can also gate it behind consent or block it with a content security policy.
Is this different from the Meta or Google pixel?
Not fundamentally. It is a conversion measurement pixel of the standard kind. What is new is which company is running one and what that company is also asking you for advice about.