Google AdSense will remain on second price bidding, while Google Ad Manager (Ad Exchange inventory) evolved to a unified first-price auction. According to Google, as of September 25, 2019, Ad Exchange traffic has transitioned to a first-price auction, where the closing price is determined by the highest net bid in the auction.
Google says AdSense will remain on a second-price auction and will continue to follow the standard second-price auction logic.
AdSense and Ad Manager are the 2 Google programs for web monetization with ads.
Google AdSense is an ad network connecting advertisers with publishers. The majority of the demand come from Google Ads – CPC Bidding – but AdSense is also open to external bidders, like DV360 and other DSPs. AdSense has a second-price auction.
Google Ad Manager is an adserver, where publishers can host the ads sold directly to clients. Besides, publishers can connect exchanges like Rubicon Project or Pubmatic, can connect Adsense, or create deals with advertisers, via RTB protocol. Google Ad Manager exchange has a first-price auction.