Transaction ID (TID) is a technical identifier used in programmatic advertising auctions to link bid requests for the same ad impression that arrive through different paths. TID is part of the OpenRTB standard (Open Real-Time Bidding), which serves as the common language across the industry for conducting programmatic auctions. The standard defines the type of data exchanged between buyers and sellers and how the different stages of the auction are identified and documented.
When the same identifier is used across different stages, buyers can detect if they are being offered the same impression via multiple paths, allowing them to choose the most efficient route to purchase media. When implemented consistently, TID brings benefits to the entire ecosystem, but publishers have raised significant concerns that, in its current form, it has been used against their interests.
Although it is a technical identifier, its use and governance are tied to broader questions of how data is leveraged and how the rules of open web auctions are shaped. Due to a Prebid update, TID has become one of the hottest topics in programmatic advertising in recent months.
Publishers’ concerns and risks of misuse
The transaction ID was introduced in Prebid version 8 in 2023. By default, however, the identifier was switched off and required a separate activation. The reasoning behind this was the concern that if sensitive or valuable data travelled along with the call, third parties could exploit it without the publisher’s knowledge or consent.
In practice, this meant, for example, that through SSP X, a deal-based targeted inventory might be sold at €10 CPM, while the same user could be found via another SSP on the open market at a much lower price. Naturally, the buyer chose the cheaper path, meaning the identifier was used against the publisher’s interests. This had a direct negative impact on the publisher’s business. In addition, the information was visible to other parties beyond the final buyer – such as curation companies that could build their own products on top of this data – again to the publisher’s disadvantage.
Publishers also became concerned that buy-side players were exploiting TID by selecting which bids they would pass into the auction after running their own internal auction. As a result, publishers could not view all competing bids for their inventory, which in turn made it more challenging to create accurate pricing strategies.
How does the Prebid update affect the use of TID?
In 2025, Prebid.js version 10.9 introduced significant changes to how TID works. Previously, the same identifier was passed to all participants in the auction; however, with the update, it became bidder-specific. Each bidder now receives its own TID, and there is no longer a single shared identifier for the entire auction. This complicates auction tracking and makes it harder for buyers to manage duplication and optimise supply paths (Supply Path Optimisation, SPO). From the publishers’ perspective, however, the change can offer protection, as it limits buyers’ visibility into floor prices, individual deals, and other strategic information. At the same time, it may reduce the opportunities for buyers to provide feedback on how auctions are performing.
From a standards perspective, the issue is about consistency. The IAB Tech Lab emphasises that TID should remain the same for everyone in line with the OpenRTB standard, so that the ecosystem stays unified and comparable. Prebid, on the other hand, stresses that protecting publisher data and safeguarding revenue potential is more important than perfect uniformity. Thus, a technical issue quickly turns into a power struggle: who holds the most influence in open web auctions – buyers or sellers?
What solutions have been proposed to the TID dispute?
Several options have been suggested to address the situation. One proposal is that buyers should share more information about the course of auctions with publishers, enabling them to identify potential duplications more effectively and manage them better. Others have suggested that bidder-specific TIDs could be used under commonly agreed rules. This would give buyers a tool to control duplication without exposing all the details of the auctions.
There has also been discussion about hiding TIDs in high-value premium deals, so that sensitive information, such as floor prices or contract terms, would not be leaked and potentially misused. The latest idea to emerge is encrypted TIDs, which can only be unlocked by trusted partners. This would enhance security and provide publishers with greater control over who can access the data. At the same time, it has been emphasised that industry standards must be clarified so that all players operate under the same rules. All of the proposals share a common goal: to create a solution that reduces the risk of misuse and builds trust, without undermining the efficiency of programmatic advertising.
What does the TID debate reveal about the future of programmatic advertising?
The Transaction ID debate shows that this is not just a technical detail but a power struggle affecting the entire programmatic advertising ecosystem. The identifier determines who gets visibility into data, how revenues are distributed, and on whose terms the open web operates. From the publishers’ perspective, the issue is above all about how well they can manage their own inventory and ensure that technical solutions support fair returns—not just buyer efficiency. Buyers, meanwhile, need tools to ensure campaign effectiveness and eliminate duplication.
The final resolution will likely require compromises, but it must be built on trust between both sides. If successful, TID could evolve into a tool that supports both buyer efficiency and sustainable publisher revenue—while strengthening the role of the open web in the long term.