Published: 17 September 2026

TL;DR: AdCP (Agent Communication Protocol) is the open standard published by AgenticAdvertising.org for agent-to-agent advertising transactions. Alkimi is the marketplace infrastructure through which those transactions run. The two are complementary: AdCP defines how agents communicate; Alkimi provides the identity verification, deal record storage, and neutral infrastructure that make those communications commercially meaningful.

Buyers new to agentic advertising frequently ask whether they need AdCP or Alkimi. The question misframes the relationship. AdCP and Alkimi operate at different layers of the same system. Understanding what each one does, and what it cannot do on its own, helps buyers and publishers make sound decisions about what they need to build.

What AdCP Does

AdCP is the AdCP, published by AgenticAdvertising.org. It defines the message format and communication structure for agent-to-agent deal negotiation in advertising. When a buy-side agent sends a deal proposal to a sell-side agent, AdCP specifies what that message contains, how it is structured, and how the receiving agent should parse and respond to it.

AdCP is a protocol standard. It is analogous to other industry communication standards that define how systems talk to each other across organisational boundaries. Without a shared protocol, a buy-side agent built by one vendor cannot communicate meaningfully with a sell-side agent built by another. AdCP solves the interoperability problem at the message layer.

What AdCP does not do is provide the infrastructure through which those messages travel. It does not verify agent identities. It does not store deal records. It does not provide a neutral third party to hold the agreed terms once a deal is reached. AdCP is the standard; it requires infrastructure to become operational.

What Alkimi Does

Alkimi is the marketplace infrastructure through which AdCP-compliant agents negotiate and record deals. It provides several capabilities that a protocol standard cannot provide on its own.

Identity verification is the first. Before a buy-side agent can send a proposal through Alkimi, its identity credentials are verified. This step prevents unverified or fraudulent agents from entering negotiations. The protocol specifies the message format; the marketplace checks who is sending it.

Proposal routing is the second. Alkimi connects buy-side agents with the sell-side agents representing the inventory they are seeking. A protocol standard defines the message structure; a marketplace provides the directory and routing infrastructure that gets the message to the right counterparty.

Deal record storage and retrieval is the third. When buy-side and sell-side agents reach agreement through AdCP-compliant messages, Alkimi writes the agreed terms to a DealSheet: a bilateral deal record held by both parties. This record is timestamped, written at the moment of agreement, and accessible to both parties independently. Neither the protocol nor the agents themselves provide this record. It requires marketplace infrastructure.

Neutral custody is the fourth. Alkimi holds the deal record as a neutral marketplace with no commercial stake in the deal terms. This neutrality matters for reconciliation and dispute resolution. An infrastructure provider with a financial interest in deal outcomes is not well-placed to provide neutral record custody.

Why Buyers Need Both

A buyer deploying a buy-side agent needs AdCP compliance to ensure their agent can communicate with any sell-side agent it encounters, regardless of the vendor or platform. Without AdCP compliance, the agent is limited to counterparties using the same proprietary message format.

A buyer also needs marketplace infrastructure to verify the counterparties they are dealing with, route their proposals to the right sell-side agents, and receive a deal record that will hold up at reconciliation. AdCP compliance alone does not provide these functions.

The practical implication: buyers evaluating agentic advertising platforms should ask whether the platform is AdCP-compliant and whether it provides the additional infrastructure layers. Compliance with the protocol is necessary but not sufficient.

Why Publishers Need Both

Publishers face the same requirement from the sell-side. A sell-side agent must be AdCP-compliant to receive and parse proposals from any buy-side agent. But the publisher also needs the deal record. Without a DealSheet written at negotiation time and held independently, the publisher has no pre-delivery record of what was agreed. Their ability to reconcile delivery data and pursue any shortfall depends on having that record.

A marketplace that provides AdCP routing but stores deal records only on its own systems does not give the publisher the independent retrieval capability that makes bilateral deal ownership meaningful.

AdCP and Alkimi solve different problems. AdCP solves the interoperability problem: it gives agents a common language. Alkimi solves the infrastructure problem: it gives that common language a place to operate with verified identities, neutral custody, and bilateral deal records. Buyers and publishers need both layers in place before agentic advertising can deliver its full operational benefit.