Meta knows what you click. ChatGPT knows what you're worried about. Now they run the same plumbing.
TL;DR [show]
Between February and September 2026 OpenAI built, piece by piece, the advertising stack Meta spent a decade refining: ads in ChatGPT from February 9, a self-serve ads manager and measurement pixel in May, custom audiences matched against hashed emails in July, a pixel that automatically detects and hashes customer details on advertisers' sites, a server-to-server conversions API and a one-day view-through window. Bloomberry counted about 15,000 advertiser sites running the pixel by late September, 85% of them added that month, and the business passed a $1 billion run rate in under 200 days. Meta is still far larger, and has used conversations with its own AI to target ads since December 2025 with no opt-out. The piece argues the plumbing is commodity and the input is not: a click is a revealed preference, a question to an assistant is a revealed worry, and OpenAI's protections (no ads near health or politics, chats never shared with advertisers, pixel data not 'currently' used for personalization) are policy choices in the present tense. One independent researcher found a cross-site cookie OpenAI labels as analytics that reaches the ad collector even when marketing cookies are refused; OpenAI has not explained the label. The difference between the two companies is no longer the machine. It is what the machine is fed.
Meta's advertising business runs on a short list of parts. A pixel on the advertiser's website that reports what you did there. A feature that reads the email or phone number you typed into a checkout form, hashes it, and sends it back so the visit can be matched to your account. A server-to-server pipe for the conversions the browser misses. Custom audiences, where an advertiser uploads its customer list and the platform finds those people. And attribution, so an ad you saw and did not click can still take credit for what you bought the next day. Meta did not invent all of it, but it made the set standard, and its pixel now sits on about one website in twelve.
OpenAI built the same set in about eight months.
The same parts, in order
Ads appeared in ChatGPT for logged-in adult users in the US on February 9. A self-serve ads manager and a measurement pixel followed in May. Custom audiences arrived in July: upload emails or phone numbers, matched against ChatGPT users, with a minimum of 25,000 matches. The pixel's documentationdescribes "automatic advanced matching," in which "the OpenAI Pixel automatically detects supported customer information from your website" and hashes it. Consent, unless the advertiser says otherwise, "initializes ... to `true` by default." There is a conversions API. View-through conversions use "a fixed one-day window after an eligible ad impression."
None of that is sinister in itself. It is the industry's standard kit, and an ad business without it would be the strange one. Eric Seufert, who has watched this market longer than most, called custom audiences "table stakes" and said OpenAI was executing quickly "against the well-worn Meta playbook." Several of the people running it came from Meta.
What is unusual is the speed. Bloomberry scanned two million company websites in late September and found OpenAI's pixel on roughly 15,000 of them, 85% added in September alone. OpenAI says the ads business crossed a $1 billion run rate in under 200 days. The plumbing is going in faster than anyone has installed this kind of plumbing before, and it is going in on sites you have bought from.
Different water
The pipes are the same. The water is not.
Meta learned about you from what you did in public, or near enough: what you clicked, liked, lingered on, bought. A click is a revealed preference. It says what you wanted, in a moment where you knew you were choosing.
ChatGPT learns from what you ask. OpenAI said in January that more than 230 million people a week ask it health questions. People ask it about the lump, the debt, the marriage, the test result, the thing they are not ready to tell anyone. A question is a revealed worry. It says what you were afraid of, often at an hour when you were not choosing anything at all, just trying to find out how bad it was.
OpenAI's ads help page says that with ads personalization on, ad selection can draw on "select signals from your broader ChatGPT experience," and that "if memory is on, ChatGPT may save and use memories and reference recent chats when selecting an ad." There are toggles for both. The same page commits that advertisers "never receive your chats, chat history, memories, name, email, precise location, IP address," and the company has said ads will not appear near health, mental health or political topics. Personalized ads are not offered in Europe at all, yet.
Those are real commitments, and I would rather they exist than not. They are also policy, and policy has a tense. Present tense.
The word "currently"
The measurement pixel's documentation contains this sentence: "For clarity, OpenAI does not currently use data collected via the measurement pixel for user-level personalization. If we do so in the future, we will respect this opt-out toggle." It is honest. It is also a description of a door, and of which side of it OpenAI is standing on this quarter.
In September an independent researcher who publishes as Buchodi reported a cookie called `__obi`, set by OpenAI for a year across its domains and, by his account, attached to calls to the ad collector when a signed-in user visits an advertiser running the pixel. OpenAI's cookie policy lists it under analytics. Analytics is the category users are usually allowed to keep when they refuse marketing, so declining ad tracking does not remove it. His finding is one person's, on Chrome for Android. He infers, but did not observe, that it links the visit back to the ChatGPT account. Nobody has published a second reproduction. When he asked OpenAI why the cookie is labelled analytics, support told him the findings would be shared internally, and that is still the answer.
You do not need his finding to see the shape, though. A view-through conversion means crediting an ad for a purchase made without a click. To do that, something has to connect the person who bought on the advertiser's site to the person who saw the ad inside ChatGPT. That is my inference, not OpenAI's statement, but it is the inference the feature requires. Hashed emails from the advanced-matching pixel would do it. So would a cookie. Last December I wrote that AI answers break the attribution chain that used to follow a traveller from search to booking, because the intent signal disappears upstream of any tracking. This is the assistant rebuilding that chain with itself at the top.
Scale, which still favours Meta
None of this makes OpenAI the bigger watcher. Meta reports 3.6 billion people using its apps every day; ChatGPT has about 1.2 billion a week. Meta's pixel is on vastly more of the web. And since December 2025 Meta has used conversations with its own AI assistant to personalize the content and ads people see, with no opt-out short of not using Meta AI. The company that perfected the click is already reading the questions.
So the comparison is not who sees more. It is what each one sees. Meta built the most efficient machine ever made for turning attention into sales, and fed it a decade of clicks. OpenAI has now built the same machine and is feeding it something no ad network has had at this scale: the version of you that types at 2am because it cannot ask anyone else.
The plumbing was always going to be commodity. Every platform that sells ads inevitably converges on the same pipes. The part that is not commodity is what you poured in before you knew there were pipes, and the only thing standing between those questions and that machine is a sentence with "currently" in it.
—TJ