An ad exchange is the digital marketplace where DSPs (advertiser side) and SSPs (publisher side) connect to trade ad inventory through real-time bidding auctions. When a publisher's app or page has an ad slot, the SSP sends a bid request to one or more ad exchanges. Each exchange broadcasts the request to its connected DSPs. The highest bid wins, and the exchange awards the impression.
Major mobile ad exchanges in 2026
- Google AdX (Google Ad Manager exchange) — the largest by volume. Tight integration with Google Ad Manager (publishers) + Google DV360 (advertisers).
- Magnite — formed from 2020 merger of Rubicon Project + Telaria + SpotX. Strong in CTV + video alongside mobile.
- OpenX — independent exchange, premium publisher focus.
- PubMatic — publicly-traded SSP + exchange. Strong mobile + emerging-markets coverage.
- Index Exchange — independent, strong in header bidding.
- AppLovin Exchange (ALX) — mobile-app-focused exchange tightly integrated with AppLovin's mediation stack.
The auction mechanics are defined by the OpenRTB protocol. Bid requests carry inventory metadata + audience signals; bid responses carry creative URL + price. Most modern exchanges run first-price auctions (winner pays their bid) rather than second-price, after the industry shifted in 2017-2019 to address transparency concerns.
Exchange vs SSP — easy to confuse: SSPs are publisher-side platforms (where the publisher manages their inventory). Exchanges are the auction venues (where SSPs route impressions and DSPs bid). In 2026, most major SSP companies also operate their own exchanges (Magnite, PubMatic, OpenX run both functions), but you'll see them referred to as one or the other depending on which side of the marketplace is being discussed.