What protocols let advertising agents transact directly with publisher agents?

Two protocol layers govern how advertising agents transact directly with publisher agents: A2A (communication) and AAMP (deal vocabulary). A2A, published by Google in 2025, defines how agents discover each other and exchange structured messages. AAMP, advanced by the IAB Tech Lab, defines what a machine-readable advertising deal must contain. Above both protocols sits the marketplace layer, where deals are recorded and governed. A platform needs all three layers to support genuine agent-to-agent transactions.

Two open specifications govern how advertising agents transact directly with publisher agents: A2A at the communication layer, and the Agentic Advertising Management Protocols (AAMP) at the deal vocabulary layer. These protocols address different parts of the problem, and both are necessary for direct agent-to-agent transactions to work reliably.

At a glance

AAMP: Agentic Advertising Management Protocols — the IAB Tech Lab standard (2025) defining the minimum schema a machine-readable advertising deal must contain for agent-to-agent interoperability.

A2A protocol: Google's 2025 specification for peer-to-peer communication between AI agents — the messaging layer over which deal enquiries and responses travel.

MCP: Model Context Protocol — Anthropic's 2024 specification for how an AI agent connects to external tools and data sources.

OpenRTB: The IAB Tech Lab standard for real-time auction-based impression buying; covers auction-time bidding, while AAMP covers direct deal negotiation above the auction layer.

What does A2A handle?

A2A (Agent-to-Agent protocol), published by Google in April 2025, defines how agents discover each other, establish authenticated connections, and exchange structured messages. It is the transport and authentication layer. A buyer agent using A2A can find a publisher agent, confirm its identity, and send it a structured message without requiring a bespoke integration between the two platforms.

A2A does not define what an advertising deal looks like. It defines how agents talk to each other. The content of that conversation is determined by higher-level specifications.

What does AAMP handle?

The Agentic Advertising Management Protocols, developed by the IAB Tech Lab, defines the vocabulary and structure of agent-to-agent advertising deals. It specifies what fields a deal record must contain: price terms, inventory specifications, targeting constraints, volume commitments, approval requirements and audit metadata. It defines how agents express counter-offers, how acceptance is recorded, and what a disputed deal flag looks like.

AAMP sits above A2A. Two agents that both implement A2A can communicate. Two agents that both implement AAMP within that communication can negotiate a compliant advertising deal. Without AAMP, agents can talk to each other but have no shared language for deal terms.

Why are both protocols necessary but not sufficient?

A2A and AAMP together define the protocol stack for agent-to-agent communication and deal formation. They do not define the governance infrastructure: where the deal record lives, who has access to it, and how disputes are resolved when buyer and publisher agents reach conflicting records of what was agreed.

That governance layer requires a marketplace: a neutral third-party platform that holds the deal record, makes it available to both sides, and provides the infrastructure for programmatic dispute resolution. A marketplace that implements A2A and AAMP at the protocol level and provides bilateral deal record governance is the full stack required for agent-to-agent transactions to be trustworthy at scale.

What is the current state of protocol adoption?

As of October 2026, A2A support has been announced across the major agency platforms and several SSP and DSP providers. Production deployments of agent-to-agent deal negotiation using A2A are operating in pilot at specialist platforms.

AAMP adoption is earlier stage. The specification is under active development by the IAB Tech Lab, with a stable draft published in mid-2025 and comment periods ongoing. Platforms implementing AAMP ahead of the final standard are making a bet on the specification's direction; that is not unusual in early protocol adoption cycles.

What does incomplete protocol adoption mean for buyers today?

A buyer operating a buying agent today will encounter publisher agents at varying stages of protocol adoption. Some publisher platforms speak A2A and AAMP. Others speak proprietary APIs. Others still require human account management for deal negotiation.

This heterogeneity is the practical constraint on agent-to-agent advertising at scale in 2026. Buyers need their buying agent to handle multiple integration modes: native A2A plus AAMP where available, proprietary API where necessary, and human escalation where neither is available.

The buying agent's configuration, not its AI capability, is the current operational challenge. What protocol does each publisher support? What deal record does each marketplace generate? What is the escalation path when agent-to-agent negotiation is not possible? These are infrastructure decisions, not technology decisions, and they need to be made before deployment.

Frequently asked questions

What is A2A protocol and how is it used in advertising?

A2A is Google's 2025 specification for agent-to-agent communication. In advertising, it provides the messaging format that buying and publisher agents use to exchange deal enquiries, counter-proposals, and acceptances during deal negotiation.

How do AI shopping and media-buying agents negotiate prices with publishers?

A media-buying agent sends a structured deal enquiry to a publisher agent specifying price range, audience requirements, and brand safety constraints. The publisher agent responds with available terms. Both agents iterate until they commit or the buying agent escalates to a human.

How does agent-to-agent negotiation reduce intermediaries in ad buying?

When a buying agent and publisher agent transact directly through a shared marketplace, the bilateral deal record replaces the relay of terms through separate SSP and DSP systems. The neutral marketplace holds the record; neither side needs the other's proprietary deal management system.