A2A Explained: The Agent-to-Agent Protocol

A2A, the Agent-to-Agent protocol, is an open standard for AI agents to communicate and delegate tasks to one another. It originated at Google and, since 17 August 2026, is a hosted project of the Agentic AI Foundation, the Linux Foundation body that also holds MCP. In the context of agentic commerce it is best understood as a coordination layer: it is not a commerce protocol in itself, but the substrate that buyer and merchant agents use to talk, and that payment standards build on.

Where it stands

The mechanism is an agent card: a structured description of what an agent can do and how to reach it, which an agent publishes and other agents read to discover capabilities and delegate work without a human brokering the handoff. A2A reached v1.0, its first stable specification, on 12 March 2026, adding multi-protocol bindings and version negotiation, enterprise multi-tenancy, signed agent cards for cryptographic identity verification, and a migration path for early adopters. (The signatures field on the AgentCard itself predates v1.0, landing in v0.3.0 in July 2025, so v1.0 stabilized it rather than introduced it.) The current specification release is the v1.0.1 patch of 28 May 2026, a set of spec bug fixes; the language SDKs carry higher version numbers of their own, which are not specification versions. At the protocol’s one-year mark in April 2026 the Linux Foundation reported more than 150 supporting organizations, up from around 50 a year earlier, including AWS, Cisco, Google, IBM, Microsoft, Salesforce, SAP, and ServiceNow, with the protocol embedded in Azure AI Foundry, Copilot Studio, and Amazon Bedrock AgentCore.

Who governs it, and why the August move matters

A2A launched at Google in April 2025 and was donated to the Linux Foundation the same year. On 17 August 2026 it moved again, out of the Linux Foundation’s broader portfolio and into the Agentic AI Foundation (AAIF) as a hosted project, alongside MCP, Block’s goose, AGENTS.md, agentgateway, and Agent Router. On 22 October 2026 AAIF added four more projects (Anthropic’s Agent Skills, OpenAI’s Open Responses, Hugging Face’s OpenEnv, and Alibaba’s OpenSandbox), bringing it to ten. Each project keeps its own maintainers, specification process, and release cadence. A2A’s own announcement, published on 27 August 2026, describes the governance tier as a Growth Stage project at AAIF.

The practical significance is narrow but real. The two protocols agentic commerce leans on most, MCP for tool and data access and A2A for agent-to-agent coordination, are now governed in the same place under the same neutral structure. That removes a category of vendor risk for anyone building multi-agent systems, and it is the clearest instance so far of the pattern the rest of 2026 has followed: standards moving out of their sponsors and into neutral bodies. What it does not do is change the specification, the maintainers, or anything a builder integrates against today.

The Linux Foundation is explicit that A2A and MCP are complementary rather than competing: A2A defines how agents communicate and coordinate across organizational boundaries, while MCP defines how an agent connects to tools and data sources. Now that both sit under AAIF, that division of labor is a governance position as well as a technical one.

The formal standards world has since taken a position on A2A too. On 8 October 2026 the IETF approved the charter of a new working group, Agent Communication Protocols (agentproto), to define a common baseline agentic dialog management protocol and reference architecture. It does not replace A2A: the charter names A2A and MCP as existing application-layer protocols that can carry its dialog context “using their own mechanisms,” and leaves any change to A2A with A2A’s own maintainers. Its milestones run to March 2028, so for builders this is a signal to watch rather than anything to integrate; see MCP Explained for the history of the group.

Its role in commerce

A2A shows up underneath the payment layer rather than at the checkout. Two connections matter. First, AP2, the payment-authorization standard, is designed to be used as an extension of A2A (and of MCP), so the signed-mandate machinery can ride on top of agent-to-agent messaging. Second, an A2A x402 extension brings x402-style stablecoin payments to agent-to-agent interactions, built by Google with Coinbase, the Ethereum Foundation, and MetaMask. In both cases A2A handles how the agents coordinate, and the commerce or payment specifics live in an extension on top.

How to hold it in your head

Keep the layers separate: A2A is how agents talk and delegate, MCP is how an agent discovers tools, and the commerce and payment protocols (ACP, UCP, AP2, x402, MPP) run the actual transaction on top. A2A is the most behind-the-scenes of the agentic commerce acronyms, which is why it usually appears as a foundation other protocols extend rather than something a merchant integrates directly. For the full map, see the protocol stack.