A2A (Agent2Agent): how it relates to agent payment protocols

Steward: A2A Project at the Linux Foundation
Status: Live
Primary source: Agent2Agent (A2A) Protocol Specification (external link)

What it is

gives an a published , a JSON document that describes its skills, endpoints and security schemes, plus a task model that a client agent drives across a network boundary. Tasks carry messages and artifacts and move through states such as input-required. The public Agent Card is served at /.well-known/agent-card.json, and the specification separates the application protocol from its JSON-RPC, gRPC and HTTP transport bindings. ^{Source [1]}

A2A is often compared with : MCP connects one application to the tools and data it uses, while A2A connects agents to other agents. ^{Source [2]}

Status

is live and published as a Linux Foundation project. ^{Source [1]} On 2025-08-29 the LF AI and Data Foundation announced that IBM’s Communication Protocol (not OpenAI’s ACP) was joining forces with A2A. ^{Source [3]}

How it relates to the eight

In the payments orbit is a transport and a container for .

AP2 calls itself an open extension for A2A (and for and UCP), and its Python samples run merchant, credentials provider and payment processor agents that talk over A2A. ^{Source [4, 5]}
For x402, the a2a-x402 repository defines the x402 Payments Extension v0.1 with the extension URI https://github.com/google-a2a/a2a-x402/v0.1 and the payment states payment-required, payment-submitted and payment-completed. ^{Source [6, 7]} x402 v2 carries a matching A2A transport that signals payment with the task state input-required and x402.payment.status metadata. ^{Source [8]}
UCP defines an A2A binding for its checkout , and businesses that support it publish an endpoint. ^{Source [9]}
ERC-8004 registration files can list an A2A service that points to an agent card, and feedback entries can reference A2A skills, contextId and taskId. ^{Source [10]}

No direct A2A binding was found in the cloned specs of ACP, MPP, or Mastercard Pay.

Relations at a glance

How A2A (Agent2Agent) relates to each protocol
Protocol	Relation	Note
AP2	Complements	AP2 describes itself as an open extension for A2A, and its samples run merchant, credentials provider and processor agents over A2A.
x402	Complements	The a2a-x402 extension v0.1 and the x402 A2A transport carry x402 payment states inside A2A task messages.
UCP	Complements	UCP's checkout capability has an A2A binding; businesses using it publish an agent card endpoint.
ERC-8004: Trustless Agents	Compatible with	ERC-8004 registration files can point to an A2A agent card, and feedback can reference A2A skills, contextId and taskId.

Back to the orbit

Sources

Agent2Agent (A2A) Protocol Specification (external link)A2A Project (Linux Foundation). Specification, primary source. Accessed 2026-10-11.
A survey of agent interoperability protocols: MCP, ACP, A2A and ANP (external link)arXiv. Paper, primary source. Published 2025-05-04. Accessed 2026-10-11.
ACP Joins Forces with A2A (external link)LF AI & Data Foundation. Announcement, primary source. Published 2025-08-29. Accessed 2026-10-11.
AP2 - Agent Payments Protocol Documentation (external link)Google (google-agentic-commerce). Documentation, primary source. Accessed 2026-10-11.
AP2 repository (README, METADATA, LICENSE) at e1ea56d (external link)Google (google-agentic-commerce). Repository, primary source. Published 2026-04-29. Accessed 2026-10-11.
A2A Protocol: x402 Payments Extension v0.1 (external link)Google (google-agentic-commerce). Specification, primary source. Published 2025-09-16. Accessed 2026-10-11.
a2a-x402 repository (A2A x402 extension) (external link)Google Agentic Commerce. Repository, primary source. Accessed 2026-10-10.
x402 A2A transport (V2) (external link)x402 Foundation. Specification, primary source. Accessed 2026-10-10.
Checkout A2A binding (v2026-08-25) (external link)UCP Authors. Specification, primary source. Published 2026-08-25. Accessed 2026-10-11.
ERC-8004: Trustless Agents (specification source, ERCS/erc-8004.md) (external link)Ethereum ERCs repository. Specification, primary source. Published 2026-01-25. Accessed 2026-10-11.