Ad buying between buyer and seller agents

Media buying has two speeds. Auctions for single impressions already run between machines in milliseconds under OpenRTB. Direct and guaranteed deals still move through RFPs, spreadsheets, email and insertion orders. That second path is where buyer and seller agents are arriving, and IAB Tech Lab has been publishing the specifications for it through 2026. The open work is less about message formats and more about who each agent represents, what it may commit, and what both sides can prove later.

How it works today

Auctions. OpenRTB is the protocol for real-time bidding on single impressions. The 2.6 line is current, with dated releases such as v2.6-202606 in June 2026. OpenRTB 3.0 is a layered model that uses AdCOM as its domain layer. The SupplyChain object in OpenRTB 2.6 lists every entity in the direct flow of payment for an impression.

Direct and guaranteed deals. A typical buy runs like this:

1. An agency sends publishers an RFP: budget, flight dates, audience, formats, goals.
2. Each publisher answers with a proposal, often a spreadsheet of packages and rates.
3. The two sides negotiate by email and calls.
4. They sign an insertion order under standard terms. The long-standing reference is the 4A’s/IAB Standard Terms and Conditions, version 3.0 of 2010. IAB finalized newer modular terms in May 2026, including a Direct Buy Addendum and order-specific terms for insertion orders.
5. The deal is set up in the ad platforms. OpenDirect 2.1 defines an API for automated guaranteed buying, and the Deals API, finalized in February 2026, carries deal terms from the system that created a deal to the system that receives it.

IAB Tech Lab itself describes the step from RFP to buy commitment as largely manual.

Supply-chain checks. ads.txt lets a publisher list the companies authorized to sell its inventory. app-ads.txt does the same for apps. sellers.json lets an exchange or SSP publish who its sellers and intermediaries are.

Agentic work at IAB Tech Lab. In January 2026 IAB Tech Lab published an Agentic Roadmap that extends its existing standards with MCP, A2A and gRPC, and planned open-source buyer and seller reference agents. Since then it has:

Item	What it is	Status (September 2026)
Agentic Real Time Framework (ARTF)	Containerized agent services that run inside a host platform and modify the bidstream	v1.0 final; first named Agentic RTB Framework
Buyer Agent and Seller Agent	Apache 2.0 reference implementations using OpenDirect 2.1, MCP, and A2A over JSON-RPC 2.0	Published on GitHub
Agent Registry	Registers MCP and A2A agents with a category and maturity level	Launched March 2026
AAMP 3.0 with OpenProposal	Standard flow from a seller’s published packages to a buyer’s commitment: publish, discover, compare, qualify, negotiate, bind and execute, report	OpenProposal in public comment until 22 October 2026

Separately, AgenticAdvertising.org publishes the Ad Context Protocol (AdCP), an Apache 2.0 protocol that also uses MCP and A2A. It is not an IAB Tech Lab specification.

The agent-to-agent version

Illustrative. An agency’s buyer agent, working for one advertiser, sends a publisher’s seller agent a brief:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "SendMessage",
  "params": {
    "message": {
      "messageId": "msg-rfp-q1-0412",
      "role": "ROLE_USER",
      "parts": [
        { "text": "Request for proposal: streaming video, guaranteed delivery, Q1 flight." },
        {
          "data": {
            "advertiser": "Example Outdoor Co",
            "flight": { "start": "2027-01-11", "end": "2027-03-28" },
            "budgetUsd": 180000,
            "geo": ["US", "CA"],
            "formats": ["video-15s", "video-30s"],
            "dealType": "programmatic-guaranteed",
            "responseDue": "2026-10-09"
          },
          "mediaType": "application/json"
        }
      ]
    }
  }
}

From there:

1. The seller agent returns two proposals as artifacts, each with impressions, a CPM and the package definitions it publishes.
2. The buyer agent asks for a lower CPM on a longer flight. The seller agent can go part of the way within its own floor, and marks one condition that needs a person’s approval.
3. Each side’s owner approves the final terms, within limits set in advance.
4. The seller agent creates the deal and sends its terms through the Deals API. Impressions then flow through the normal auction path with the deal ID attached.
5. Delivery reports come back on the same task until the flight ends.

What has to be true

Identity. The buyer agent needs proof that the seller agent may sell this publisher’s inventory. ads.txt and sellers.json already answer that for exchanges and SSPs; the same check should cover an agent endpoint, for example by the publisher naming its agent in a file on its own domain or signing its Agent Card with a key tied to that domain. The seller needs to know which agency is calling and which advertiser it represents. IAB’s Agent Registry lists agents; a listing is a claim about an agent, and the buyer still has to confirm the agent speaks for this publisher.

Authority. An insertion order is a contract. Each agent needs a written limit: maximum budget, rate floor or ceiling, allowed deal types, brand-safety exclusions, and which terms it may accept without a person. The agency’s own authority from the advertiser matters too.

Record. Delivery disputes, makegoods and audits all return to what was agreed. Both sides need the brief, each proposal, each concession and the final commitment in a form that neither can later edit. Privacy signals such as GPP strings must travel with the deal from the start.

Standards involved: OpenRTB 2.6 and AdCOM, OpenDirect 2.1, the Deals API, ads.txt and sellers.json, AAMP and OpenProposal, A2A and MCP. On whether a contract formed by agents binds the parties, see the legal NDA use case.

Where Emissar fits

IAB Tech Lab and AdCP already supply the domain vocabulary and reference agents, so most of this stack exists without Emissar. Where it could apply:

• Verify (in development) checks which agent is calling, who built it and whose behalf it acts on, across whatever registry listed it.
• Mandate (spec in progress) is a proposal for the written limit above: budget, rates and terms an agent may accept for one principal.
• Ledger (spec in progress) is a signed record of proposals and commitments that both sides can retrieve.
• Front Door (open to design partners) could serve a publisher that wants to receive agent RFPs without running its own agent.

Settle does not fit today: media is usually paid through billing cycles after delivery.

Open questions

• OpenProposal is still in public comment. Its final shape will decide what an agent-made commitment contains.
• How should ads.txt, sellers.json, registry listings and signed Agent Cards combine into one check a buyer agent can run?
• AAMP and AdCP both build on MCP and A2A. Will buyers need to support both?
• Which terms should never be accepted by an agent alone, such as cancellation rights or liability caps?
• How are makegoods negotiated when delivery falls short, and who approves them?