IAB Tech Lab yesterday released the final version of its Programmatic Auction Definitions document, a structured glossary and process primer designed to give every participant in the programmatic supply chain - from brand teams to sell-side engineers - a common understanding of how digital advertising auctions work. The document is the product of a multi-organization effort that began in 2025 and concluded a public comment period in late February 2026.

The release comes after a process that drew in some of the largest names in the advertising measurement and buying community. According to IAB Tech Lab, the Media Rating Council, Omnicom Media Group, and a coalition of industry bodies including ANA, WFA, 4A's, and IAB Tech Lab came together in 2025 to address a long-standing problem: the mechanics of programmatic auctions were poorly understood, inconsistently described, and effectively invisible to many of the people whose budgets depended on them.

The Programmatic Auction Definitions document was developed in collaboration with IAB Tech Lab's Programmatic Supply Chain subgroup. A public comment period ran from January through February 27, 2026. The final version released today incorporates feedback gathered during that period.

Why now, and why it matters

The programmatic advertising market processes hundreds of billions of impressions each day. Yet the vocabulary used to describe how those impressions are bought and sold has remained fragmented - sellers, buyers, and intermediaries frequently working from different mental models of what an "auction" even means, or what happens between a page load and an ad appearing on a screen.

The MRC's Auction Standards Working Group addressed this with its Digital Advertising Auction Transparency Standards, which aim, according to the document, to "promote transparency around auction rules and scoring along with reporting and standardization where possible and appropriate, to ensure that auction rules and outcomes are understood for all parties."

IAB Tech Lab was specifically asked to produce supplemental material covering the OpenRTB use case - the protocol that governs the vast majority of automated programmatic transactions globally. The result is a 12-step workflow document paired with 15 defined terms. Its stated audience is brand and agency leaders who want to understand programmatic auction mechanics, though the technical depth makes it useful for ad operations and product teams as well.

PPC Land covered the specification when it entered public comment in January 2026, noting at the time that the document arrived amid sustained industry focus on auction transparency and supply chain efficiency.

The 15 defined terms

The document provides precise definitions for terms that the industry has used loosely for years. Understanding these definitions is practical for anyone negotiating, trafficking, or auditing programmatic campaigns.

Ad Context covers the set of surrounding environmental factors, content attributes, and user attributes of a digital session used to determine the relevance, safety, and suitability of an ad placement. This definition is notable because it explicitly links context to suitability - a distinction that has become central to brand safety debates.

Ad Inventory Controller is defined as an entity that holds the right of sale for an ad opportunity. This is not necessarily the publisher themselves; in multi-hop supply chains, this right can be delegated.

Ad Opportunity - also referred to as an Impression Opportunity - is the point at which a user activates an ad placement and triggers an ad request by loading web or app content, or streaming audio or video content.

Ad Placement refers to the specific area or moment within digital content - such as a webpage, video, or audio stream - designated as a container for an advertisement to be served.

Ad Rendering describes the act of the ad creative being painted on the screen, streamed, or added to the Document Object Model within the context it is intended to display in. The document makes a point of specifying that rendering does not always indicate viewability - a distinction with real implications for impression counting and billing.

Ad Request is the information about the ad impression to be auctioned.

Ad Request Initiators are the systems that create ad requests, at the instruction of the ad inventory owner.

Auction is defined as the process an entity receiving competing bids uses to qualify, evaluate, and decide which to pursue and which to ignore, with decisions based on the relative value of each bid.

Auctioneer is a system that solicits bids to buy inventory from demand partners.

Bid Price is what the demand-side platform is willing to pay.

Bid Response is the information about the ad from a buying platform and the offer that the buyer is willing to make for the impression.

Bid Solicitation is an ad-request initiator requesting that bid requests be generated and bid responses solicited from upstream systems.

Billable Event is an event that signals that the auction is billable.

Buying Platform is an entity that services advertising campaigns by evaluating - based on the information provided in ad requests - impression opportunities that meet campaign requirements, and making offers to purchase them.

Final Auctioneer is the system that determines which bid, if any, is accepted and is given the impression opportunity. This is often the publisher's ad server.

Loss URL (lurl) is the bid loss notification URL provided in the bid response by the selling platform that can be called after the auction to convey to a buying platform why they lost.

Received Bids are returned bids to the selling platform that are technically qualified to enter an auction.

Returned Bids are all bids returned to the auctioneer, pre-qualification. The distinction between returned and received bids matters: returned bids include everything that comes back, including responses that fail validation.

Selling Platform is an entity that routes ad requests from an ad request initiator to potential additional entities in the supply chain.

Unauthorized Ad Request is an ad request that does not meet ads.txt and sellers.json validation, indicating that the seller is not authorized by the inventory owner to sell the listed inventory.

The 12-step auction workflow

Beyond definitions, the document lays out a 12-step workflow that traces an ad impression from inventory setup through final transaction recording. Each step is discrete and sequential, though in practice some happen in milliseconds and others are asynchronous.

Step 0 - Ad Inventory Setup establishes the baseline. Ad inventory owners configure placements detailing where and when they want ads shown, integrated with a final auctioneer - typically the publisher's ad server. This server holds the definitive configuration for ad slots and is ultimately responsible for filling them, whether through directly-sold campaigns or by reaching out to programmatic partners. The auction process begins when a slot cannot be immediately filled with a direct-sold campaign.

Step 1 - Ad Request Initiation is where the ad request initiator requests that selling platforms solicit bids. This step very commonly uses the OpenRTB specification. With programmatic demand, ad request initiators typically call multiple selling platforms simultaneously. Each selling platform may in turn call additional selling platforms in a single request initiation - a structure the document calls a multi-hop supply chain. Selling platform A sells to selling platform B, which sells to buying platform A. The document notes that more than two or three hops is rare and generally suboptimal.

Step 2 - Ad Request Validation is where the selling platform receives the request and validates it. This covers supply chain authorization by the seller - including validating ads.txt, sellers.json, and the supply chain object - as well as validation of the device, IDs, and other business process checks. If the ad request is malformed or unauthorized, processing stops.

Step 3 - Ad Request Enrichment allows the selling platform to enhance the inventory owner's ad request with additional features, such as audience data based on the relationship with the intended recipient.

Step 4 - Bid Solicitation sends the ad request to eligible demand partners. Not every request goes to every demand partner. Exclusions may reflect business rules - a demand partner may not want traffic from certain geographies - or algorithmic decisions, such as a system predicting no response from a given buying system.

Step 5 - Bid is where buying platforms make their own determinations about which bids to return. This may involve evaluating multiple campaigns and their relative value. The solicitation results in four general conditions: no response, an error, a no-bid response, or a response with one or more bids. Responses that include bids typically contain a bid price - most often net of fees - and where applicable, a deal ID.

Step 6 - Validate Returned Bids covers technical validation of bids received from buying platforms. Error cases include responses received after a timeout has expired, unparsable responses, invalid values in the response, and missing fields required by the seller. The result is zero or more bids the seller can evaluate further.

Step 7 - Qualifying Received Bids applies business rules to technically valid bids. This includes checking bid price against pricing rules, verifying the bid's seat and the advertiser against seller allow and block lists (covering categories, ad domains, buyer seats, creative IDs), and validating that bids with deal IDs conform to deal terms.

Step 8 - Competition is where each bid competes within the auction at a determined auction price. Price may incorporate buying platform fees or discounts to establish an auction price that represents the net price for the seller. A winner - or in some cases, multiple winners - is selected.

Step 9 - Return Winning Bids allows intermediary auctioneers to forward more than one accepted bid to upstream partners, some or all of which may be sent to the final auctioneer. Buying platforms may include URLs in their bid responses that sellers can use to signal loss reasons to losing buyers via a standard loss reason code.

Step 10 - Waiting for Ad Rendering is where the final auctioneer performs a final set of validation and qualification steps, selects a winner, and attempts to deliver the winning ad. Even after the final auctioneer selects an ad, the user may have left the page or paused content, or technical reasons may prevent rendering. Critically, the document notes that the selling platform's winning bid does not equate to the winning bid for the final auctioneer. A publisher's ad server may receive the winning bid from the selling platform and never render it, because another business rule filled the slot instead - such as directly-sold demand or a subsequent programmatic auction achieving higher yield.

Step 11 - Transaction Recording covers what happens after rendering notifications and transaction signals are received. Fees, clearing price, billable price, and other telemetry are recorded. Notification is returned to the buying platform for record keeping.

Step 12 - Reconciliation acknowledges that most companies participating in auctions have monthly processes in which numbers between systems are matched, and discrepancies managed. The document does not cover this in detail but recognizes it as a standard operational reality.

Price is not the only factor

One of the more practically useful sections addresses what drives auction outcomes beyond raw bid price. According to IAB Tech Lab, few auctions execute purely based on cost, though price is often a heavily weighted signal.

Media owners may prioritize campaigns sold directly by their sales teams over programmatic bids regardless of cost. Buying platforms may prioritize bids for campaigns that are not meeting their delivery requirements over higher-priced ones. All parties may prioritize bids based on their broader business and revenue goals. A party may decrease the relative value of a bid due to historical ad retrieval errors with the buyer - for example, if the creative is more likely to cause a VAST error. Meeting competitive separation requirements matters too: a broadcaster may have a deal with an advertiser to not show competitor ads in the same ad break. Frequency capping requirements - such as not showing an ad more than three times a day to the same user - apply as well. All parties may filter based on acceptable ad formats, advertisers, and other criteria.

This section directly addresses a common frustration among buyers: losing auctions without understanding why. The framework provides at least a structural vocabulary for asking those questions.

Who contributed

According to IAB Tech Lab, the Programmatic Auction Definitions document was developed by the Programmatic Auction Definitions subgroup, with inputs from the Programmatic Supply Chain Working Group and Commit Group. Significant contributions came from Matt Davies of Bidswitch, Scott Kay of Microsoft, Simon Sorensen of Freewheel, Jana Meron of Lioness Strategies, Amit Shetty of Fox, Paul Bannister of Raptive, Chris Kane of Jounce Media, Neal Richter of Amazon Ads, David Sidman of Videostorm, and Brian May. The document was authored and led by Jill Wittkopp, VP of Product at IAB Tech Lab.

The document is licensed under a Creative Commons Attribution 3.0 License.

Industry context

The release lands at a moment when auction transparency has become one of the more actively contested topics in digital advertising. The Media Rating Council issued draft Digital Advertising Auction Transparency Standards in September 2025, with comments accepted through October 20, 2025. Those standards represent the first formal framework for auction disclosure requirements across display, video, audio, search, social, retail media, and CTV channels.

Check My Ads Institute submitted formal comments on October 20, 2025 challenging the MRC proposal, warning that it risked legitimizing opacity and creating a two-tier system that favored large closed-loop platforms. The IAB Tech Lab Programmatic Auction Definitions document operates separately from that accreditation debate, but both efforts share the same underlying premise - that auction participants deserve to understand the mechanics of the systems processing their money.

The supply chain has also seen significant technical disputes over the same period. IAB Tech Lab challenged Prebid's transaction ID changes in August 2025, declaring that the modifications materially violated the OpenRTB specification by creating bidder-specific identifiers rather than maintaining consistent transaction IDs across all auction participants. Publishers drove those Prebid changes citing yield protection concerns. The dispute illustrated precisely the kind of vocabulary gap the Programmatic Auction Definitions document is designed to address - different parties operating from different assumptions about what the auction is supposed to guarantee.

IAB Tech Lab released its Deals API specification on December 5, 2025, addressing transparency gaps in curated programmatic deals - another layer of the same supply chain the Auction Definitions document now helps explain structurally.

For buyers trying to understand what is happening to their money between the moment a bid is submitted and the moment an ad either renders or does not, the Programmatic Auction Definitions provides a concrete reference. It does not resolve the competitive and contractual questions that occupy most of the industry's transparency debates, but it does provide a shared starting point. As PPC Land has documented across multiple coverage threads on IAB Tech Lab's agentic roadmapand OpenRTB standards development, the organization's ability to produce durable standards depends heavily on whether practitioners across the ecosystem adopt a common vocabulary - which is precisely the problem this document targets.

Timeline

Summary

Who: IAB Technology Laboratory, in collaboration with the Media Rating Council, Omnicom Media Group, ANA, WFA, 4A's, and a Programmatic Supply Chain subgroup including contributors from Bidswitch, Microsoft, Freewheel, Fox, Raptive, Jounce Media, Amazon Ads, and others. The document was led by Jill Wittkopp, VP of Product at IAB Tech Lab.

What: The final version of the Programmatic Auction Definitions document - a 12-step auction workflow guide and glossary of 15 defined terms covering the OpenRTB programmatic supply chain, from ad inventory setup through transaction reconciliation. The document is designed to give brand and agency leaders a common vocabulary and understanding of how digital advertising auctions actually operate.

When: The collaboration began in 2025. The document entered public comment on January 29, 2026, with a comment period running through February 27, 2026. The final version was released today, June 26, 2026.

Where: The document covers the OpenRTB use case within programmatic advertising, applying to digital advertising auctions across display, video, audio, and connected television environments. It is published on the IAB Tech Lab website and in the IABTechLab GitHub repository under a Creative Commons Attribution 3.0 License.

Why: Questions about how programmatic auctions work - why buyers lose, what factors beyond price influence outcomes, and what each step in the supply chain does - have persisted for years without a clear, shared answer. The Media Rating Council's Digital Advertising Auction Transparency Standards created a formal demand for supplemental material on the OpenRTB use case. The Programmatic Auction Definitions document responds to that demand by establishing common vocabulary and a step-by-step process map that all ecosystem participants can reference.