The landscape of AI agent protocols is experiencing an unprecedented proliferation phase, reminiscent of the early web or the dawn of REST services. Over the past eighteen months, four significant protocols have emerged: Anthropic's Model Context Protocol (MCP), IBM Research's Agent Communication Protocol (ACP), Google's Agent2Agent (A2A), and the independent Agent Network Protocol (ANP). At first glance, this looks like chaos, but a closer examination reveals a clear layering. Each protocol addresses a different stack level rather than competing for the same slot. The real challenge today is not which protocol to choose, but what is still missing: peer-to-peer transport for agents that must communicate across cloud boundaries, home networks, and edge deployments.
The Tool-Calling Layer
MCP has already won the tool-calling battle. It defines how a model discovers the functions a server exposes, how to invoke them, and how to interpret the response. It is a typed RPC contract between a model client and a tool server running over HTTP. The Linux Foundation has confirmed over 10,000 active public MCP servers and 164 million monthly Python SDK downloads as of April 2026. Standardization at this layer is effectively complete. Development teams can adopt MCP today with very low risk, a point also emphasized in the operational guide to the Cyber Resilience Act, where integrating standardized protocols is a compliance requirement.
Sponsored Protocol
The Task Coordination Layer
A2A fills a gap that MCP leaves open. While 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 A2A to the Linux Foundation in June 2025, and enterprise AI teams have broadly adopted it because it addresses a real need. For multi-agent coordination, adopting A2A today is reasonable, with the expectation that the protocol will evolve. This aligns with the recommendations of the NIS2 cybersecurity regulation, which mandates a security-oriented and interoperable architectural approach.
The Lightweight Messaging and Discovery Layer
ACP and ANP complete the stack. ACP is a lightweight, stateless message envelope format useful when A2A's full task lifecycle management is unnecessary. ANP focuses on discovery and identity, using Decentralized Identifiers (DIDs) and JSON-LD graphs to describe agent capabilities, laying the groundwork for decentralized agent marketplaces without a central registry. The emerging stack is clear: capability discovery via ANP, task coordination via A2A, tool calls via MCP, and lightweight messaging via ACP. These layers complement each other, not compete.
Sponsored Protocol
The Remaining Transport Problem
Every protocol described so far runs over HTTP. This reflects the origins of the teams: research labs, API providers, and enterprise software companies for which HTTP is an unquestioned assumption. But in production, HTTP assumes a reachable server. 88% of networked devices sit behind NAT (Network Address Translation), where there is no reachable server without a relay. For agent fleets that need to route tasks directly between peers across cloud boundaries, home networks, and edge deployments, this centralization forces every message through relay infrastructure, adding latency, cost, and a single point of failure. The application-layer protocols solve the semantics of what agents say to each other; they do not solve how agents find each other and establish direct connections. This is a session-layer problem (Layer 5 of the OSI model) that none of MCP, A2A, ACP, or ANP address.
Sponsored Protocol
The technologies to solve it already exist. UDP hole-punching with STUN (Session Traversal Utilities for NAT) works for roughly 70% of network topologies. X25519 Diffie-Hellman and AES-256-GCM provide authenticated encryption at the tunnel level without a certificate authority. QUIC (RFC 9000) or custom sliding-window protocols over UDP provide reliable delivery without TCP's head-of-line blocking. These are the same primitives used by WireGuard for VPN tunnels and WebRTC for browser-to-browser media streams. What differs in the agent context is capability-based routing: an agent should be able to query "which peers have real-time foreign exchange data?" and receive a list of currently active specialist agents. This is closer to a service registry than to DNS, and it is a natural extension of ANP's design philosophy applied to the transport layer.
A handful of projects are assembling these pieces. Pilot Protocol has the most complete published specification, with an IETF Internet-Draft covering addressing, tunnel establishment, and NAT traversal for agent networks. libp2p provides a battle-tested foundation with similar primitives. The IETF's QUIC working group is developing NAT traversal extensions that will be relevant here. According to authoritative sources like Wikipedia, the A2A protocol is already being deployed in enterprise environments, but the transport layer remains an open research area.
Sponsored Protocol
How Convergence Will Happen
The HTTP-based application protocols (MCP, A2A) are converging on stable versions. The next twelve months will bring production hardening, security improvements, stateless MCP servers for horizontal scaling, and better A2A federation. The tool-calling and task coordination layers are largely solved. The transport layer is 18 to 24 months behind. Expect a period of implementation diversity as teams experiment with different approaches to peer-to-peer agent networking, followed by consolidation around a small number of implementations once empirical data on performance and reliability accumulates. The IETF and W3C standardization tracks will likely produce something in the 2027-2028 window, by which time one or two open-source implementations will have accrued enough production deployments to establish de facto standards ahead of the formal specification.
Sponsored Protocol
For engineering leaders making architecture decisions today, the practical implication is layered adoption. The application-layer protocols are stable enough to build on. MCP adoption now is low-risk. A2A adoption for multi-agent coordination is reasonable. The transport layer is where you either build something custom and plan to replace it, or evaluate early implementations knowing the space is still moving. The teams that will have the most leverage when the transport layer stabilizes are the ones that designed their agent systems with a clean separation between application semantics (MCP, A2A) and transport (whatever sits below). Clean separation is cheap to implement now and expensive to retrofit later, a lesson the microservices era taught anyone who tried to add observability or circuit breaking to systems that had none.
