Programmatic
Last look
Last look is an auction advantage in which one bidder sees the best competing bid before bidding, so it can win by bidding just slightly more.
In an auction with last look, one participant goes after everyone else and knows the price to beat. That lets it win whenever it values the impression even a cent above the top competitor, and it can win at the lowest possible price.
The term is most closely linked to Google's ad stack. When publishers used header bidding, the winning header bid was passed into Google's ad server as a price, and AdX could then compete against that price, effectively a last look. Together with dynamic allocation, this helped AdX win more impressions.
Google said it ended last look when it moved Ad Manager to a unified first-price auction in 2019. Last look and related practices were examined in the United States v. Google case. More broadly, any system where one party sees others' bids first, including some ad mediation setups, raises the same fairness concern.
Think of it like this
Last look is like a card game in which one player may peek at everyone else's hand before placing their bet.
An example
The best header bid is US$2.00 CPM. With last look, the exchange bids US$2.01 and wins; without it, it would have had to guess and might have bid US$1.80 and lost.
Related terms
Dynamic allocation
Dynamic allocation is a Google Ad Manager feature that lets Google's ad exchange compete in real time against a publisher's other non-guaranteed campaigns for each impression.
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.
Header bidding
Header bidding is a technique where a publisher offers each ad impression to many SSPs and exchanges simultaneously before calling its ad server, so all buyers compete at once.
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.
Antitrust in ad tech
Antitrust in ad tech refers to competition-law cases and investigations examining whether dominant companies, especially Google, have monopolised or abused their position in the technology used to buy and sell ads.