[mathteddybear]

I guess not really. The ad exchange is sort of an auction of auctions; for bare efficiency, every participating network submits only their top two candidates. This is communicated to ad networks; I guess, there is no obligation that the networks pass the bids of their advertisers unchanged. Google has some secret sausage there.

To Google Ads advertisers, Google says "you participate in a second-price auction, competing with other Google Ads advertisers and other networks; if you win you will pay the bid of the runner-up, which is the second highest bid from the Google Ads unless another network submits a bid in between" and that holds true.

To publishers, Google says "the price is determined in a second-price auction, every ad network submits up to two bids"

IANAL but it may be considered as an anti-trust, because it is the owner of the ad exchange who could decide if that obligation exists (regardless of whether it could be plausibly enforced).