Sure, but as long as the adtech providers each have their own stable IDs for you, they can still use `google_push` to link their corresponding stable IDs together, uniquely identify you, and merge their respective profiles.

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Page View #1:

- Acorp: google_gid=qwerty, google_push=foo

- Bcorp: google_gid=asdfgh, google_push=foo

- Ccorp: google_gid=zxcvbn, google_push=foo

By exchanging their `google_gid` values corresponding to the page load with shared `google_push` value foo, Acorp, Bcorp, and Ccorp can identify you as user qwerty-asdfgh-zxcvbn.

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Page View #2:

- Acorp: google_gid=qwerty, google_push=bar

- Bcorp: google_gid=asdfgh, google_push=bar

- Ccorp: google_gid=zxcvbn, google_push=bar

By exchanging their `google_gid` values corresponding to the page load with shared `google_push` value bar, Acorp, Bcorp, and Ccorp can still identify you as user qwerty-asdfgh-zxcvbn, even though the `google_push` value has changed.

I now see your point, thanks. I was thinking this “google_push” is probably not unique (a.k.a many users could have the same) but the adtech providers could check the ids + timestamps to help with the match. NB: Google is not syncing with everyone on the same page view so the adtech providers have to be lucky enough to be synced on the same page view. Another question is: what is the “google_push” entropy?

Having worked in adtech, I can tell you the adtech providers probably don’t do that, for those reasons: 1) those adtech providers are usually competitors 2) if they work together, they can already sync their user ids directly together (so using google id is not necessary).

So I don’t think Google intentions were malign here on this particular point (contrary to Brave communication and all the press coverage). But yes, Google shouldn’t add entropy by sending the same “page view id” to different adtech providers. Note that Google is “better” than the others here: every other adtech providers send the same user id to each partner (persistant identifier, not session or page view like google). And those providers are sometimes quite big: for example, AppNexus or Criteo trackers are also everywhere on the web. Overall, it’s the RTB system with all those cookie syncs that shouldn’t exist, and except for the “google_push” argument, Brave study is quite good (they are just explaining how the adtech world works).