Tech Lab contests proposed modifications to Prebid's transaction identification system
The IAB Tech Lab, a non-profit consortium that develops foundational technical standards for digital advertising, has announced potential specification updates to address the ongoing controversy surrounding Prebid's transaction ID (TID) modifications.
The modification in question affects how buyers identify when multiple bid requests represent the same impression opportunity. Prebid recently modified its implementation to generate unique transaction IDs for each bidder, rather than maintaining a consistent identifier across all exchanges. This change eliminates the primary deduplication mechanism that demand-side platforms relied upon to identify duplicate auction opportunities.
The controversy centers on transaction identifiers, which serve as unique auction identifiers across all suppliers throughout the entire supply chain. The IAB Tech Lab criticized the latest changes in Prebid's implementation of the TID field last week, stating that the new approach is materially non-compliant with the OpenRTB specification and risks undermining the integrity of open technical standards in the programmatic advertising ecosystem.
The IAB Tech Lab has emphasized its commitment to finding industry solutions rather than unilateral implementations and announced plans to convene a dedicated forum with publishers, buyers, and technology partners. The forum is expected to explore technical alternatives such as optional transaction ID scoping, publisher-controlled identifier policies, or enhanced privacy controls within the existing framework.
This controversy highlights broader challenges in balancing transparency, privacy, and technical standards in programmatic advertising. The changes implement bidder-specific transaction identifiers in several key areas, including the ortb2Imp.ext.tid field and ortb2.source.tid. The modifications could formalize privacy protections while maintaining cross-exchange transaction visibility.
The IAB Tech Lab operates under the leadership of CEO Anthony Katsur. In August 2025, the IAB Technology Laboratory issued a statement declaring that the recent changes in Prebid's implementation of the TID field materially violate the OpenRTB specification. This statement represents a significant escalation in tensions between the standards body and the header bidding wrapper.
The modification has generated significant discussion across programmatic advertising channels, with concerns about duplicate bids, wasted spend, and higher costs. The IAB Tech Lab launched the PAIR protocol in September 2024 for first-party data matching and the Trusted Server initiative in March 2024 for enhanced publisher control. In February 2025, the IAB Tech Lab clarified video placement definitions to improve implementation.
The IAB Tech Lab is committed to addressing these concerns and finding solutions that maintain the integrity of the programmatic advertising ecosystem while also promoting transparency, privacy, and technical standards. The dedicated forum announced by the IAB Tech Lab will likely provide a platform for industry stakeholders to collaborate and find solutions to the challenges posed by the TID controversy.
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