Interoperability is the ability of two systems built by different companies to exchange information and then make use of what was received. The IEEE Standard Computer Dictionary, published in 1990, defined it as the ability of two or more systems or components to exchange information "and to use the information that has been exchanged". Those are two requirements, not one. A demand-side platform that can parse a bid request but misreads what its fields mean has achieved transmission, not interoperability. The concept carries unusual weight in advertising because no single company owns the pipeline. One impression passes through a publisher's ad server, a supply-side platform, an exchange, a demand-side platform, a verification vendor and a measurement provider before money changes hands, and each of those is a separate business running its own code. Absent shared conventions, every pair of companies would need a bespoke integration, and the number of integrations would grow with the square of the number of participants.

Four layers where it is decided

The first layer is technical. Systems need a shared transport and encoding before anything else is possible. OpenRTB defines the objects that make up a bid request and a bid response. VAST describes a video advertisement to a player. Two platforms that both implement OpenRTB 2.6 can trade without either writing code specific to the other.

The second is semantic, and it fails more quietly. Shared syntax is worthless if the parties disagree about meaning. AdCOM supplies common object definitions used across IAB Tech Lab specifications, and content taxonomies fix the vocabulary for categories and audiences. Where one field carries two readings, the result is not an error message but a silent mismatch that surfaces weeks later in reconciliation.

The third is identity. A browser cookie, a mobile advertising identifier, a connected television identifier and a hashed email address are unrelated strings with no common key. Universal identifiers such as LiveRamp's RampID, Unified ID 2.0 and the ID5 ID supply a shared token that multiple parties can recognise. Cryptographic protocols take a different route: the Publisher Advertiser Identity Reconciliation protocol, or PAIR, uses commutative encryption so that two clean rooms operated by rival companies can find their overlap without either decrypting the other's list.

The fourth is governance. Consent frameworks, certification schemes and contracts determine whether an exchange is permitted, not merely possible. The Global Privacy Platform functions as a transport layer for privacy signals, carrying strings from IAB Europe's Transparency and Consent Framework, IAB Canada's framework, the MSPA United States national string and individual state strings inside a single structure whose header acts as a table of contents.

What it looks like inside a bid request

The abstraction becomes concrete in OpenRTB 2.x objects. The Regs object carries the GPP string, added in the November 2022 release alongside the older TCF and US Privacy signals. The eids array carries extended identifiers with a source domain and a declared match method, which is how a universal ID reaches a bidder. The SupplyChain object lists every intermediary that touched the impression, and sellers.json plus ads.txt let a buyer check that the seller claiming the inventory is authorised to sell it. None of these is a product. Each is a convention that stops working the moment enough participants ignore it.

Google's own migration illustrates the pull toward convergence. The company retired its proprietary Authorized Buyers bidding protocol on 15 February 2025, moving all bid requests to OpenRTB and removing the largest remaining exception to the standard on the open web.

Origin and evolution

The word predates advertising. It entered technical use in military and telecommunications engineering, where separately procured systems had to work together in the field, and the 1990 IEEE dictionary fixed the definition still quoted. European law adopted a near-identical formulation in the Software Copyright Directive, describing the ability to exchange information and mutually use what has been exchanged. ISO's vocabulary added a user-facing test: transfer between functional units should require little or no knowledge of their individual characteristics.

Advertising arrived late. Version 1.0 of the OpenRTB block list specification was published in December 2010, and the IAB adopted OpenRTB as a formal standard with version 2.1 in January 2012. Supply chain conventions followed the fraud crises of the mid-2010s, with ads.txt, sellers.json and the SupplyChain object filling gaps that ordinary trading had not exposed. OpenRTB 2.6, released in April 2022, added ad pods for connected television. Version 3.0, whose final document carries a June 2020 date, restructured the protocol but never displaced the 2.x line.

Privacy signalling standardised next. The Global Privacy Platform string specification reached version 1.0 on 28 September 2022, with encoding clarifications added in November 2023 and implementation guidelines finalised by the Global Privacy Working Group in February 2025. Identity followed on 26 September 2024, when IAB Tech Lab launched PAIR, folding in the earlier Open Private Join and Activation specification. Andrew Knox of Decentriq, quoted in the launch materials, described the merger of the two standards as a step forward for clean room interoperability.

Why it matters to advertisers and publishers

Interoperability is a cost line before it is a principle. Every integration a vendor cannot inherit from a standard becomes engineering work, maintenance and an eventual point of failure. Standards bodies make the arithmetic explicit: IAB Tech Lab completed 79 initiatives during 2024 with input from more than 800 member companies, and announced 31 specification releases or updates for 2025.

Where standards are thin, the cost shows up as unspent budget. IAB Europe found that 70% of buyers cited the absence of retail media standards as a barrier to investment, and the trade body issued updated pan-European definitions on 26 March 2025 to address it. Measurement is the other pressure point. DoubleVerify research released on 18 November 2025 reported that 65% of advertisers had brand suitability concerns in walled gardens, rising to 74% among organisations with 5,000 to 9,999 employees.

Limitations and disputes

The most public rupture came on 27 August 2025, when IAB Tech Lab declared that Prebid's implementation of bidder-specific transaction identifiers materially violated the OpenRTB specification. Anthony Katsur, the standards body's chief executive, said the approach risked undermining conventions that are "critical to interoperability across the programmatic ecosystem". Prebid's stated motivation was a publisher privacy concern: consistent transaction identifiers let buyers stitch data across exchanges. Both positions are coherent, and they cannot both be satisfied by the same field. The dispute had commercial consequences. The Trade Desk launched its OpenAds platform on 2 October 2025, after the identifier change, a pattern of building proprietary infrastructure when a standard cannot be controlled.

Mandated interoperability draws sharper objections. Article 6(7) of the EU's Digital Markets Act requires operating system gatekeepers to open interoperability free of charge on terms equivalent to those their own services enjoy. Apple, designated for iOS on 5 September 2023 and for iPadOS on 29 April 2024, published a statement on 24 September 2025arguing that it must meet almost every request "even if they create serious risks for our users", citing one seeking the full content of a user's notifications. The European Commission specified how the obligation should work in two decisions dated 19 March 2025, holding that interoperability must be effective in practice and that equal terms require equivalent functionality rather than an identical technical solution. Apple's published process runs eligibility assessment within 20 working days, a project plan within 40, and development windows of six, 12 or 18 months depending on classification.

A third criticism is proliferation. Standards intended to reduce fragmentation can add to it. The Ad Context Protocol launched on 15 October 2025 and drew immediate argument about whether the sector needed another protocol while existing ones remained underused.

Interoperability and adjacent terms

Compatibility means one system works with another, often asymmetrically and often by design of the larger party. Interoperability implies a shared specification neither side controls. Portability concerns moving data or an account out of a service, a one-time export rather than an ongoing exchange; DMA Articles 6(9) and 6(10) cover portability separately from Article 6(7) interoperability. Integration describes a specific connection between two named systems, which may be entirely bespoke. Open source describes a licence on code, not a guarantee that the code follows any standard.

Recent developments

Agentic infrastructure is where the question now sits. The Ad Context Protocol, built on Anthropic's Model Context Protocol and governed by the nonprofit AgenticAdvertising.org, launched with six founding members and 23 further participants, defining nine core tasks across the campaign lifecycle. IAB Tech Lab published an agentic roadmap on 6 January 2026 that extends OpenRTB, AdCOM, VAST and OpenDirect rather than replacing them, and named the umbrella initiative AAMP on 26 February 2026, with separate task forces for execution protocols, interoperability standards and an Agent Registry that reached ten entries by 11 March 2026.

Regulatory interoperability produced its first consumer-visible result in the same period. WhatsApp opened third-party messaging in Europe on 14 November 2025 under Article 7 of the DMA, initially with BirdyChat and Haiket, using either a client-to-server-to-client model or a proxy server while preserving end-to-end encryption. BirdyChat completed a full European launch on 5 May 2026, with roughly 40 million European WhatsApp users shown the integration in settings.

Timeline

  • 1990: The IEEE Standard Computer Dictionary publishes the definition of interoperability still in general use
  • December 2010: Version 1.0 of the OpenRTB block list specification is released
  • January 2012: The IAB adopts OpenRTB as a formal standard with version 2.1
  • June 2020: The final OpenRTB 3.0 document is dated; version 2.x remains the working standard
  • April 2022: OpenRTB 2.6 adds ad pods for connected television
  • 28 September 2022: The Global Privacy Platform string specification reaches version 1.0
  • November 2022: GPP transport through the OpenRTB Regs object is included in the monthly release
  • 5 September 2023: The European Commission designates Apple as a gatekeeper for iOS
  • 29 April 2024: Apple is designated a gatekeeper for iPadOS
  • 26 September 2024: IAB Tech Lab launches the PAIR protocol, superseding Open Private Join and Activation
  • 15 February 2025: Google retires its proprietary Authorized Buyers bidding protocol in favour of OpenRTB
  • 19 March 2025: The Commission issues two specification decisions interpreting Article 6(7) of the DMA
  • 26 March 2025: IAB Europe publishes updated pan-European retail media definitions
  • 27 August 2025: IAB Tech Lab states that Prebid's transaction identifier changes violate OpenRTB
  • 24 September 2025: Apple publishes its objections to DMA interoperability requests
  • 2 October 2025: The Trade Desk launches OpenAds
  • 15 October 2025: The Ad Context Protocol launches with six founding members
  • 13 November 2025: IAB Tech Lab opens its Agentic RTB Framework version 1.0 for public comment
  • 14 November 2025: WhatsApp enables third-party messaging in Europe under Article 7 of the DMA
  • 17 December 2025: Japan's Mobile Software Competition Act takes effect with an equivalence standard modelled on Article 6(7)
  • 6 January 2026: IAB Tech Lab publishes an agentic roadmap extending OpenRTB, AdCOM, VAST and OpenDirect
  • 26 February 2026: The AAMP umbrella initiative is named, with an interoperability standards task force
  • 11 March 2026: The IAB Tech Lab Agent Registry reaches ten registered entries
  • 5 May 2026: BirdyChat completes its European launch with full WhatsApp interoperability

Summary

Who: IAB Tech Lab, IAB Europe, Prebid.org, the W3C and AgenticAdvertising.org author the technical standards. The European Commission and the Japan Fair Trade Commission mandate interoperability where markets have not produced it. Exchanges, demand-side platforms, identity vendors, clean room operators and measurement firms implement it or route around it.

What: The ability of separately built systems to exchange information and act on what they receive, resolved across four layers: technical transport, semantic agreement on field meaning, identity resolution, and governance covering consent and permission.

When: The IEEE definition dates from 1990. Advertising's core specifications followed from December 2010, with privacy signalling standardised in September 2022, clean room matching in September 2024, and agentic protocols from October 2025 onward.

Where: Global, though the regulatory strand is concentrated in the European Union under the Digital Markets Act and in Japan under the Mobile Software Competition Act.

Why: Without shared conventions, the number of bilateral integrations required to run a supply chain grows faster than the number of participants, and costs rise while match rates and measurement quality fall. Interoperability is also contested, because the party with the most inventory or the most data has the least to gain from letting others read it.