Prebid.js announced 3 days ago a breaking change. To “encourage fairer auctions, Prebid will randomize the order bidders are called by default.” This means that the bidders have a fair auction in place.
Publishers still have the option to setup an order for the bidders, like it was since the beginning.
Prebid.js is a Header Bidding solution for publishers, created by Appnexus, that gives back control to the publishers and allows multiple exchanges to participate in one auction. Is also an open source solution, that allows publishers build their own tech on top of it.