Programmatic
First-price auction
A first-price auction is an auction in which the highest bidder wins and pays exactly what they bid, which is now the standard model in programmatic advertising.
In a first-price auction, what you bid is what you pay. If you bid US$5 CPM and win, you pay US$5 (plus any fees). This is simple and transparent, but it means bidders have an incentive to bid below their true value to avoid overpaying.
Programmatic moved from second-price to first-price auctions in the late 2010s. Header bidding made second-price rules messy, because the winner of one auction was then compared with others, and some exchanges were quietly manipulating second-price clearing. Google completed its move of Ad Manager to a unified first-price auction in 2019, and most of the industry followed.
The consequence was bid shading: DSPs now use algorithms that estimate the lowest price likely to win and bid near that, rather than bidding full value. Buyers study the bid landscape to decide how aggressive to be; publishers watch whether shading pushes prices down.
Think of it like this
A first-price auction is like a sealed-envelope property sale: the highest offer wins and pays exactly what was written down.
An example
Three DSPs bid US$2.10, US$2.80 and US$3.30 CPM. The US$3.30 bidder wins and pays US$3.30, even though US$2.81 would also have won.
Related terms
Second-price auction
A second-price auction is one in which the highest bidder wins but pays just above the second-highest bid (or the floor), which was the original standard in real-time bidding.
Bid shading
Bid shading is a technique DSPs use in first-price auctions to lower a bid automatically toward the price actually needed to win, so advertisers do not overpay.
Auction dynamics
Auction dynamics are the rules and behaviours that decide who wins programmatic ad auctions and at what price, including auction type, floors, fees, bid shading and bid order.
Unified auction
A unified auction is a single auction in which all demand sources, such as direct campaigns, header bidders and exchanges, compete for an impression under the same rules at the same time.
Floor price (reserve price)
A floor price is the minimum bid a publisher will accept for an impression; bids below the floor are rejected, even if they are the highest bid in the auction.