Editorial illustration for A2A introduces Agent Cards, task lifecycle states and three sync modes
A2A introduces Agent Cards, task lifecycle states and...
A2A introduces Agent Cards, task lifecycle states and three sync modes
The story of distributed computing reads like a litany of standards that eventually settle into a few winners. CORBA, DCOM, Java RMI and early SOAP vied for enterprise integration in the late‑1990s; REST slipped in later, lean and HTTP‑native, and gradually took the lead. Real‑time messaging followed a similar arc: XMPP, IRC and a slew of proprietary protocols splintered the market until MQTT and WebSockets each carved out a niche.
Now the AI agent ecosystem is in the thick of its own proliferation phase. Four protocols have surfaced in the past eighteen months: Model Context Protocol (MCP) from Anthropic in late 2024, Agent Communication Protocol (ACP) from IBM Research in March 2025, Agent2Agent (A2A) from Google in April 2025, and the Agent Network Protocol (ANP) from an independent working group. The W3C AI Agent Protocol Community Group has opened a standards track, the IETF is reviewing transport drafts, and conferences host workshops on interoperability.
New GitHub repos appear weekly, each claiming to solve the agent communication problem. Understanding which pieces will coalesce—and how fast—has tangible implications for the architectures teams are building today.
Where MCP defines how an agent calls a tool, A2A defines how two agents delegate a task. It introduces Agent Cards (capability advertisements), task lifecycle states, and three interaction modes: Synchronous, streaming, and asynchronous. Google donated it to the Linux Foundation in June 2025, and enterprise AI teams have adopted it broadly because it fills a real gap that MCP leaves open.
Lightweight, stateless, designed for agent-to-agent message exchange without A2A's full coordination semantics. It is useful in systems where simple message passing suffices and A2A's task lifecycle overhead is unnecessary. It uses Decentralized Identifiers (DIDs) for agent identity and JSON-LD graphs for capability descriptions, providing a foundation for decentralized agent marketplaces where no central registry is required.
The stack that is emerging: Capability discovery via ANP or simpler registries, task coordination via A2A, tool calls via MCP, and lightweight messaging via ACP for cases that do not require full task lifecycle management. The transport problem that remains Every protocol in this list runs over HTTP. This reflects where the protocols came from: Research teams, API providers, and enterprise software companies building systems where HTTP is an unquestioned assumption.
Why this matters A2A’s Agent Cards, task lifecycle states, and three interaction modes extend the coordination layer that MCP introduced for tool calling. By advertising capabilities and allowing agents to delegate tasks synchronously, via streaming, or asynchronously, the framework promises a more structured approach to multi‑agent workflows. This mirrors the earlier consolidation of distributed‑computing protocols—where REST supplanted CORBA, DCOM, RMI, and SOAP—suggesting a possible narrowing of integration patterns.
Google’s donation of A2A to the Linux Foundation in June 2025 adds an open‑source pedigree that could ease adoption among developers. Yet, the article leaves open whether the new lifecycle semantics will integrate smoothly with existing AI orchestration stacks, or if additional standards will emerge to fill gaps left by the current description. We remain cautious: the utility of Agent Cards hinges on real‑world tooling and community support, both of which are still uncertain.
For founders and researchers, the announcement signals a shift toward formalized agent collaboration, but practical impact will depend on how quickly the ecosystem embraces the model and resolves any interoperability challenges.
Further Reading
- Understanding A2A — The protocol for agent collaboration - Google Developer Forums
- Announcing the Agent2Agent Protocol (A2A) - Google Developers Blog
- A2A Protocol Explained: How AI agents communicate across systems - CodiLime
- A2A Protocol Explained - Hugging Face
- Google A2A Protocol: How Agent-to-Agent Coordination Works - Atlan
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