A mediation platform is software that decides which of several advertising sources fills an ad slot inside a mobile app. The developer builds one mediation software development kit (SDK) into the app, and the platform then calls ad networks, exchanges and bidders on its behalf, compares what each is prepared to pay and hands the impression to the winner. It exists because no single network fills every request at the best price, and because hard-coding a network into an app once meant resubmitting it to Apple whenever a partner changed. AppLovin's MAX, Unity's LevelPlay, Google's AdMob mediation and Digital Turbine's DT FairBid are the best known. In connected television (CTV), server-side platforms such as Magnite's SpringServe now use the word for a related function.

How a mediation platform decides

Alongside the mediation SDK, the developer installs an adapter for each network, a thin layer of code translating between the two SDKs. Configuration lives on the platform's servers, so allocations change without an app update.

When the app needs an ad, say a rewarded video before a bonus level, the platform matches the request against the developer's rules. In AdMob these are mediation groups, targeted by platform, ad format and country. If several match, the group with the lowest priority number is chosen; groups never fall through to one another, and unmatched requests go to a default group, according to Google's AdMob help centre.

Inside a group, the waterfall calls networks one at a time, ordered by average effective cost per thousand impressions (eCPM), a historical estimate rather than a live price. It is the same sequential logic that governs backfill. AdMob can pull each network's reported eCPM through its reporting interface and reorder the list twice a day, country by country. Google Ad Manager's version sorts networks by estimated CPM alongside the real-time Ad Exchange price: its documentation shows one network at $5.75 above the exchange at $4.00, three more between $3.50 and $2.00, and drops any network priced below the exchange. Each call may wait between 1 and 60 seconds. The chain as a whole has no timeout.

In-app bidding, also called the unified auction, asks every participating source at once. Before the request goes out, each network's adapter produces a signal, an opaque token describing what its SDK knows about the device and the ads it holds; in Google's SDK a method called collectSignals does this. The token travels in the bid request - for Google's Authorized Buyers, in an extension field named buyer_generated_request_data - and the winning response carries rendering data for the buyer's own SDK, plus a declared ad submitted for creative review. Bidders answer only when they have an ad to show.

Most stacks run both. AdMob slots the top bid into the waterfall at its price, according to its documentation. Suppose a bidder offers $14 for a rewarded view in Germany while a waterfall network carries a $16 estimate. The waterfall network is tried first and serves if it fills, even if the price it later reports falls below $14. That gap between estimates and bids is why the industry has pushed toward pure bidding.

Developers configure the stack; companies that also operate ad networks run the platforms, and demand-side platforms (DSPs) reach the inventory through exchanges. Display & Video 360 (DV360) added "app mediation partners" as an inventory source in April 2024, covering AdMost, AppLovin MAX, Chartboost Mediation, DT FairBid, TopOn and Unity LevelPlay, with a fee buyers must accept. Because one app may be sold by dozens of partners, IAB Tech Lab published app-ads.txt in March 2019, a file on the developer's website listing each authorised seller as DIRECT or RESELLER.

From aggregators to auctions

The idea began with iPhone apps. AdWhirl, which raised $1 million in June 2009, let developers switch between networks such as AdMob, Jumptap and Millennial Media without resubmitting to Apple, according to TechCrunch. AdMob bought its assets that August, two months after threatening to cut aggregators off, and Google agreed to buy AdMob for $750 million later that year. Google moved developers to AdMob Mediation from May 2012 and closed AdWhirl on September 30, 2013.

Waterfalls dominated until 2018. MoPub, then owned by Twitter, put Advanced Bidding into closed alpha in February 2018. Google opened a beta of AdMob Open Bidding that March with OpenX, Smaato and Index Exchange. "The winner is always the highest paying advertiser," Sissie Hsiao, Google's vice-president of product for mobile app advertising, told AdExchanger. Facebook Audience Network, AppLovin and Rubicon Project joined in December 2018. AppLovin, meanwhile, announced on September 5, 2018 that it had acquired MAX, an eight-person start-up founded in late 2017 by the MoPub co-founder Jim Payne.

Apple's tracking changes hastened the shift. In October 2020 Facebook said Audience Network would accept only bids on iOS from the second quarter of 2021, because waterfalls grow harder to manage without device identifiers, according to AdExchanger. ironSource had forecast that 70% of its mediation traffic would run through bidding by the end of 2020.

Consolidation followed. Digital Turbine completed its purchase of Fyber, owner of FairBid, on May 25, 2021. AppLovin agreed to buy MoPub for $1.05 billion in cash in October 2021, closed on January 3, 2022 and shut MoPub on March 31, moving publishers to MAX. Unity completed its merger with ironSource, and with it LevelPlay, on November 7, 2022. The buy side pushed too: DV360 stopped bidding on multiple waterfall calls for app inventory on October 23, 2024.

Why it matters

For developers, the mediation layer sets the price of nearly every impression. Google cited Shimmer Games reporting a 36% revenue increase after reordering sources in its July 2025 AdMob update, a vendor-supplied figure.

For advertisers, the issue is concentration. Adam Foroughi, AppLovin's chief executive, wrote in February 2026 that MAX reaches more than one billion daily active users and that most of AppLovin's own ads deliver through it. Unity's counsel described MAX in a September 2026 letter as handling well over a majority of in-app auctions, by count and by spend. App campaigns bought through most DSPs therefore land in a few auctions run by companies that also sell media.

The platforms also feed measurement: impression-level revenue underpins each user's lifetime value, and Adjust launched user-level ad revenue reporting in March 2019 with ironSource and Fyber as sources.

Limitations and disputes

The central criticism is structural: the largest platforms belong to companies whose own networks bid in the auctions they run, and the operator sees every competing price. On September 28, 2026 AppLovin petitioned San Francisco Superior Court, alleging that Unity's Ad Quality SDK, bundled into LevelPlay SDK 8.9.0 in May 2025, reads per-impression MAX revenue, waterfall data and screen-touch coordinates in apps running MAX, and asked for collection to stop within five business days. The rivals have bid into each other's platforms under a header bidding agreement since October 13, 2021. Gary Bornstein, Unity's counsel at Cravath, Swaine & Moore, wrote that "Ad Quality does not collect any data from AppLovin".

Waterfalls add latency, and every network means another SDK and adapter, adding weight and points of failure. Mediation cannot rescue a winner that breaks: AdMob rewarded video on Android failed to render for about 188 hoursbetween August 20 and August 28, 2026, and because AdMob kept winning auctions, no other network could step in.

Privacy regulators have focused on how far data travels. In the Grindr case, MoPub received user data and had roughly 160 partners of its own; the Borgarting Court of Appeal upheld a NOK 65 million fine on October 21, 2025, imposed by Norway's data protection authority in December 2021.

Challengers target the closed model. Prebid, the open-source header bidding project, presents its Mobile SDK as an extra demand source inside existing stacks that takes no revenue cut. CloudX, backed by a $30 million Series A, lets DSPs bid on app supply without their own SDKs, bypassing what the analyst Ari Paparo called "one of the big SSP/ad nets".

Not the same as

Header bidding. The web practice of calling bidders in parallel. In-app bidding is its app counterpart, relying on SDK signals rather than browser code.

Supply-side platform (SSP) or exchange. An exchange sells impressions to many buyers, usually via OpenRTB. A mediation platform chooses between exchanges and networks, although AppLovin, Unity and Digital Turbine each run both.

Orchestration layer. An orchestration layer plans and books campaigns across sellers over days or weeks; mediation settles one impression in milliseconds.

Online dispute resolution platform. In European consumer law the phrase can mean the European Commission's consumer complaints portal, closed on July 20, 2025. It is unrelated to advertising.

Recent developments

Unity announced on March 26 that its ironSource Ads network would stop serving direct campaigns on April 30, while keeping LevelPlay open to all networks. On May 28, Amazon Publisher Services (APS) opened 28 additional bidders to app publishers through an InMobi SDK bridge that required no mediation changes; four unnamed gaming publishers in the beta saw APS revenue rise as much as 14 times.

CTV has adopted the label. Magnite added mediation to SpringServe in December 2025 as the layer ranking competing demand sources, and expanded it in April 2026 with Disney Advertising and MiQ among partners. JioHotstar, with 450 million monthly users, chose SpringServe for programmatic mediation in June 2026. Michael Barrett, Magnite's chief executive, has compared mediation to clearing on a stock exchange, handling settlement and compliance that buyer agents cannot manage alone.

As of September 2026, the AppLovin petition is unresolved. A hearing is scheduled for 11 a.m. Pacific time today.

Timeline

  • June 2009: AdWhirl raises $1 million to let iPhone developers switch ad networks without resubmitting apps
  • August 2009: AdMob acquires AdWhirl's assets
  • November 2009: Google agrees to acquire AdMob for $750 million
  • May 11, 2012: Google opens an import pipeline from AdWhirl to AdMob Mediation
  • September 30, 2013: AdWhirl is shut down
  • February 2018: MoPub Advanced Bidding enters closed alpha
  • March 15, 2018: Google announces a beta of AdMob Open Bidding with OpenX, Smaato and Index Exchange
  • September 5, 2018: AppLovin announces its acquisition of MAX
  • December 2018: Facebook Audience Network, AppLovin and Rubicon Project join AdMob Open Bidding
  • March 2019: IAB Tech Lab publishes the final app-ads.txt 1.0 specification
  • May 27, 2020: ironSource forecasts 70% of its mediation traffic will run through bidding by year end
  • October 2020: Facebook says Audience Network will be bidding-only on iOS from the second quarter of 2021
  • May 25, 2021: Digital Turbine completes its acquisition of Fyber
  • October 13, 2021: AppLovin and Unity sign a reciprocal header bidding agreement
  • October 2021: AppLovin agrees to buy MoPub for $1.05 billion in cash
  • January 3, 2022: AppLovin closes the MoPub acquisition
  • March 31, 2022: MoPub is sunset and publishers migrate to MAX
  • November 7, 2022: Unity completes its merger with ironSource, taking over LevelPlay
  • April 2024: DV360 adds app mediation partners as an inventory source, with a fee
  • October 23, 2024: DV360 stops bidding on multiple waterfall calls for app inventory
  • May 28, 2025: Unity's Ad Quality is bundled into LevelPlay SDK 8.9.0
  • July 7, 2025: AdMob separates bidding and waterfall ad sources and adds bidding eCPM floors
  • October 21, 2025: Borgarting Court of Appeal upholds Norway's NOK 65 million Grindr fine
  • October 2025: Prebid outlines a Mobile SDK 4.0 roadmap aimed at publisher control
  • December 2025: Magnite adds mediation to SpringServe
  • January 27, 2026: CloudX opens app inventory to DSPs without SDK integration
  • March 26, 2026: Unity announces the sunset of ironSource Ads direct demand
  • April 27, 2026: Magnite expands SpringServe mediation with AI features and new partners
  • April 30, 2026: ironSource Ads direct campaigns stop serving
  • May 28, 2026: APS introduces its InMobi SDK bridge with 28 additional bidders
  • June 4, 2026: JioHotstar selects SpringServe for programmatic mediation
  • August 20, 2026: AdMob rewarded video begins failing to render on Android, for about 188 hours
  • August 21, 2026: AppLovin sends Unity a cease-and-desist letter over Ad Quality
  • September 28, 2026: AppLovin petitions San Francisco Superior Court against Unity
  • September 30, 2026: Hearing scheduled on AppLovin's petition

Summary

Who. App developers configure mediation platforms, which are operated mainly by AppLovin (MAX), Unity (LevelPlay), Google (AdMob and Ad Manager) and Digital Turbine (DT FairBid). Ad networks, exchanges and DSPs supply the demand. In CTV, Magnite's SpringServe applies the term to server-side ad decisioning.

What. Software that receives each ad request from an app, calls competing demand sources through a sequential waterfall, a simultaneous auction or both, and awards the impression to the highest-value response.

When. Mobile ad aggregators appeared in 2009 with AdWhirl. Bidding entered mediation in 2018, accelerated after Apple's 2020 and 2021 tracking changes, and the market consolidated between 2021 and 2022. Magnite added mediation to its CTV ad server in December 2025.

Where. Inside iOS and Android apps, and increasingly in streaming environments, with configuration and auctions running on the operators' servers.

Why. Developers want every impression sold at the best available price without rebuilding their app for each new partner. Because the leading platforms also sell media, mediation raises questions about conflicts of interest, data access and concentration that are now before a court.