Header Bidding (In-App Bidding)

Header bidding (called in-app bidding in the mobile-app context) is a mediation approach where all demand sources bid simultaneously in a unified real-time auction. The name "header bidding" comes from web origins — bid requests fired from the page header before the page renders. In mobile apps, the same logic runs through the mediation SDKGlossarySDK (Software Development Kit)A packaged set of code, libraries, and tools a developer drops into an app to add a capability — the integration unit for attribution, analytics, ads, and monetizati..., but the principle is identical: every demand sourceGlossaryAd NetworkA platform that aggregates ad demand from many advertisers and matches it to publisher inventory through real-time auctions. gets a fair shot at every impressionGlossaryAd ImpressionA single instance of an ad being served to a user — the atomic unit of ad inventory. What counts as "served" vs "viewable" vs "verified" matters enormously for pricing., in real time, with the highest bid winning.

What it replaced — the classic waterfall: before header bidding, mobile mediation worked in fixed priority order. The mediation platformGlossaryAd MediationThe publisher-side layer that orchestrates multiple ad networks and demand sources to maximize eCPM — the routing infrastructure between an ad slot and the network t... called Network 1 first; if Network 1 didn't fill (or bid below floor), it called Network 2; then Network 3; until something filled. This left money on the table — Network 5 might have been willing to pay $20 eCPMGlossaryeCPM (Effective Cost Per Mille)The revenue a publisher actually earns per 1,000 ad impressions — the publisher-side counterpart to CPM, after auction dynamics, fill rates, and floor prices. for an impression that filled at $5 from Network 2 because Network 5 never got called.

How unified auction works

1. 01Impression opportunity arises — the user reaches an ad slot in your app.
2. 02All demand sources are simultaneously queried — the mediation SDK fires bid requests to every integrated SSPGlossarySupply-Side Platform (SSP)The publisher-side platform for programmatic ad selling — routes inventory to ad exchanges and manages floor prices, demand partners, and yield optimization., ad network, and SANGlossarySelf-Attributing Network (SAN)An ad network that handles its own install attribution natively — sends conversion postbacks directly to MMPs without click-tracker URL wiring. at the same moment.
3. 03Each bidder responds with a real-time bid — based on their evaluation of the impression, audience signals, and creativeGlossaryAd CreativeThe visual and audio content of an ad — video, image, copy, sound. The single most important variable in modern mobile UA, lifting IPM and lowering effective CPI. inventory.
4. 04The auction resolves — highest bid wins, the winning creative renders.

The entire auction completes in <200ms. Compared to a waterfall, the publisher gets the best bid from any source on every impression, instead of accepting the first bidder above floor.

Major in-app bidding platforms in 2026

• AppLovin MAX — the dominant mobile mediation platform. Strong fill rates, unified auction across many demand sources, robust analytics.
• ironSource LevelPlay (now Unity LevelPlay) — major competitor to AppLovin MAX. Strong fill on gaming inventory.
• Google Admob Bidding — Google's mediation product with bidding. Best for publishers already in the Google ecosystem.
• Liftoff Vungle — has a bidding-based mediation product.
• Smaato / Verve — mobile-app-focused mediation with bidding.

Most large mobile-app publishers use one primary platform with secondary integrations for diversification. Switching is painful — SDK is deeply embedded, historical data lives in the platform, demand partnerships are tied to the contract.

Implementation considerations

• SDK overhead: bidding adds latency and a few hundred KB to the app binary. Most publishers accept the trade-off given the eCPM lift.
• Demand-source onboardingGlossaryOnboardingThe first-time user experience that guides new installs from app launch to the "aha moment" — where they understand the product's value and become more likely to ret...: each new SSP / network requires SDK or s2sGlossaryServer-to-Server (S2S) PostbackA backend-to-backend HTTP request that delivers conversion event data from your servers to ad networks / MMPs — bypassing client-side SDK reliance. integration. Mature mediation platforms abstract much of this.
• Floor priceGlossaryFloor PriceThe minimum bid price a publisher will accept for a programmatic ad impression — below the floor, the impression goes unfilled (or falls through to lower-priority de... calibration: with bidding, floor prices matter differently than in waterfall. Too high = unfilled inventory; too low = leaving money on the table. Most platforms suggest optimal floors based on historical bid distribution.
• Cross-source bid normalization: some networks bid in CPMGlossaryCost Per Mille (CPM)The price an advertiser pays for 1,000 ad impressions, regardless of whether those impressions drive clicks or installs. "Mille" = Latin for 1,000., others in revenue share, others in fixed CPIGlossaryCost Per Install (CPI)The average amount an advertiser pays for a single install attributed to a campaign — total spend divided by attributed installs. deals. The mediation platform normalizes these into a single comparable bid currency.