By Kunal Nagpal, Chief Business Officer, InMobi Advertising
The programmatic advertising industry is at war with itself. Prebid has unilaterally implemented bidder-specific Transaction IDs, claiming privacy protection. The IAB Tech Lab fired back, calling it a “material violation” of OpenRTB standards. DSPs are losing critical Supply Path Optimization capabilities. Publishers are questioning whether this privacy theater serves their bottom line. The real question isn’t whether we should choose privacy over transparency, it’s whether we’re willing to build systems that deliver both.
Transaction IDs have one job: be a simple, shared auction identifier that everyone in a bid request can reference. Since OpenRTB 2.5, TiDs have functioned like a license plate for an impression, ensuring all participants reference the same transaction consistently.
Prebid broke this system in August 2025, generating different TiDs for each bidder on each request. Sure, they claim it’s about privacy and stopping DSPs from reverse-engineering supply paths. In reality? DSPs lose Supply Path Optimization tools, bid less confidently, and markets get messier.
When IAB Tech Lab’s Anthony Katsur said bidder-specific TiDs risk “undermining open technical standards,” he was calling out how overcompensating on privacy issues can hurt everyone’s bottom line. Here’s what the industry gets wrong: framing this as privacy versus transparency. True privacy protection comes from robust data governance and consent management, not from obscuring legitimate business signals that help markets function.
Without consistent Transaction IDs, DSPs lose deduplication capabilities, leading to inefficient bidding on the same impression. Supply Path Optimization becomes nearly impossible, reducing buyer confidence and bid rates. Publishers lose visibility into how their inventory is valued across different paths to market.
None of these outcomes enhance user privacy. They simply create information asymmetries that benefit intermediaries profiting from market opacity.
The Mediation Auction ID Solution
While the industry debates Transaction IDs, another transparency signal demonstrates how we can serve both buyer and seller interests: Mediation Auction IDs. A Mediation Auction ID is created at the mediation layer, where platforms like AdMob or AppLovin MAX orchestrate unified auctions. Assigning a per-auction identifier lets demand identify when multiple requests from different SSPs refer to the same impression opportunity.
We have enabled mediation auction IDs to our direct DSP partners across our SDK footprint and our initial results are clear: It helps DSPs reconcile impressions, optimize performance, and drive smarter decisioning. It enhances deduplication and clearer price evaluation as buyers understand how opportunities were valued within mediation stacks, and lower infrastructure costs.
What Makes Mediation Auction IDs the “Hero Signal”
Mediation Auction IDs check every transparency box without overexposing publisher strategy:
- Auction-scoped, not user-scoped: They expire with the event, carry no user data, and minimize privacy concerns
- Reflect real decisioning: In SDK bidding, mediation decides the winner, not the exchange
- Protect publishers: AIDs can be random and opaque—enough for deduplication and reconciliation, but not enough to reveal floors or waterfalls
- Ready to use today: They can be implemented immediately via OpenRTB ext fields
Publishers should advocate for consistent Transaction IDs and Mediation Auction IDs. Better buyer confidence translates directly to higher bid rates and eCPMs. When DSPs can properly deduplicate, optimize supply paths, and evaluate pricing across mediation stacks, they bid more aggressively and more often.
Transparency enables yield strategy validation. Publishers need visibility into how their inventory performs across different paths to market. Market efficiency benefits content creators most—systems that help buyers find and value publisher inventory more effectively ultimately drive more revenue back to content creators.
Mediation Auction IDs aren’t a reaction to evolving TiD practices—they’re complementary. A TiD gives you a shared exchange-level handle; a Mediation Auction ID gives you visibility into the auction of origin one level upstream. Together, they provide a complete view of how decisions propagate across the supply chain.
Building Markets That Work
Our focus is to deliver performance for both buyers and publishers by playing fair. This isn’t about choosing sides—it’s about creating systems where good behavior is rewarded, bad actors are exposed, and performance is maximized for everyone.
Real privacy protection comes from robust technical safeguards, proper consent management, and responsible data handling practices. It doesn’t come from eliminating legitimate business signals that help markets function.
