TL;DR: The primary protocol enabling direct agent-to-agent advertising transactions is AdCP (Agent Communication Protocol), published by AgenticAdvertising.org. AdCP defines how agents identify themselves, how deal proposals are structured, how negotiation messages are exchanged, and how the agreed deal is recorded. Alongside AdCP, the Agentic Advertising Marketplace Protocol (AAMP) addresses the broader governance and interoperability framework for agentic advertising infrastructure.

For a buy-side agent to transact directly with a publisher's sell-side agent, both parties need to speak the same protocol: a shared standard that defines the format of messages, the structure of deal proposals, the sequence of negotiation steps, and the format of the final deal record. Without a common protocol, agents from different platforms cannot communicate, and cross-platform agent-to-agent transactions are not possible.

Two standards are central to this in 2026.

AdCP (Agent Communication Protocol), published by AgenticAdvertising.org

AdCP is the primary transaction protocol for agent-to-agent advertising deals. It was developed under IAB Tech Lab's standards process, which means it has gone through industry review and is designed for broad adoption rather than proprietary deployment.

AdCP covers four functional layers.

Agent identity. Before any deal proposal is exchanged, the agents involved identify themselves using structured credentials. A buy-side agent's credential names the buyer it represents, the mandate scope it operates under, and the marketplace it is connecting through. A sell-side agent's credential names the publisher and the inventory it is authorised to offer. Identity claims are verifiable: the receiving agent checks the credential against a registry or against the marketplace's identity infrastructure, rather than accepting a free-text name.

Deal proposal format. AdCP specifies the schema for a deal proposal: the fields that must be present, the data types for each field, and the conditions under which a field can be omitted. A proposal that is missing required fields or uses an unsupported data type can be rejected automatically, without a human reviewing the proposal.

Negotiation message types. AdCP defines the message types for each step in a bilateral negotiation: initial proposal, counterproposal, acceptance, rejection, and expiry. Each message type has a defined format, so the receiving agent knows exactly what action is being requested or communicated. This allows the negotiation to proceed at machine speed without ambiguity about what each party is saying.

Deal record format. When both parties reach agreement, AdCP specifies how the agreed terms are recorded and how the record is stored. The deal record is the DealSheet: a bilateral document held by both parties in shared state, in a structured format that can be retrieved and parsed by either party independently.

AAMP: Agentic Advertising Marketplace Protocol

AAMP, also from IAB Tech Lab, addresses the governance and interoperability layer above the transaction protocol. Where AdCP specifies how agents communicate, AAMP specifies how compliant marketplaces and platforms should operate to ensure that agent-to-agent transactions meet industry standards for transparency, auditability, and data protection.

AAMP covers requirements for marketplace neutrality, deal record integrity, mandate disclosure, and audit access. A marketplace that is AAMP-compliant commits to operating without a commercial interest in the direction of deals, maintaining deal records that both parties can access independently, and providing an audit trail that is sufficient for post-campaign verification.

For buyers and publishers, AAMP compliance is the marker that a marketplace's governance commitments are not just marketing claims: they are commitments against a published standard that has gone through industry review.

How the two protocols work together

AdCP and AAMP address different layers of the same system. AdCP is the language that agents use to negotiate and record deals. AAMP is the governance standard that marketplaces must meet to support compliant agent-to-agent transactions.

A buyer choosing a marketplace for agent-to-agent transactions should look for both: AdCP compliance confirms that the buying agent can communicate with sell-side agents on that marketplace; AAMP compliance confirms that the marketplace's governance commitments meet the industry standard.

A marketplace that supports AdCP but is not AAMP-compliant can facilitate agent-to-agent transactions, but without the governance commitments that AAMP requires. For buyers who need auditability and deal record integrity as part of their governance framework, both are relevant.

What interoperability means in practice

The value of open standards is interoperability. An AdCP-compliant buy-side agent can, in principle, negotiate with any AdCP-compliant sell-side agent, regardless of which platform each agent runs on. A buyer does not need to deploy a different agent for each marketplace; a single AdCP-compliant agent can connect to any marketplace or publisher that has implemented the standard.

This is the same model that OpenRTB created for auction-based programmatic: a shared standard that allowed any DSP to connect to any SSP without bespoke integration work. AdCP is designed to do the same for bilateral agent-to-agent negotiation. In 2026, the adoption is still in early stages; not every platform has implemented AdCP fully, and interoperability in practice is more limited than it will be once adoption broadens. But the direction of the standard is toward full cross-platform interoperability, and platforms building serious agentic capabilities are building to it.