Definition
The Agent Communication Protocol (ACP) was an open standard, created by IBM Research in 2025, for letting multiple AI agents coordinate and exchange results. It is worth understanding for two reasons: it shaped how agent-to-agent communication was designed, and its story explains why that layer today has a single winner — the Agent2Agent Protocol (A2A) — rather than two competing standards.
ACP is no longer a standalone specification. It merged into A2A under the Linux Foundation in August 2025. A reader who encounters ACP in a current diagram or article is looking at a snapshot from the first half of 2025, before the consolidation, and should treat A2A as the live standard.
How It Works
ACP's distinguishing choice was to model agent interaction as plain REST over HTTP rather than the JSON-RPC approach A2A took. An agent published a metadata manifest describing its capabilities; another agent read that manifest, discovered a capable peer, and sent it a request. Responses could be synchronous for quick tasks or asynchronous for work that took longer — the same task-oriented shape that any agent-coordination protocol needs, expressed in ordinary web semantics.
The intent behind the REST-first design was accessibility: any developer who can call a REST API could integrate an ACP agent without learning a new RPC convention. The protocol was framework-agnostic, shipped with Python and TypeScript SDKs, and was built to power IBM's open-source BeeAI platform, an effort focused on agent interoperability and interpretability.
That design goal — a manifest-driven, framework-neutral way for AI agents to find and call each other — did not disappear. It was carried into A2A, which now provides the migration adapters that let former ACP and BeeAI agents participate in the unified standard.
Real-World Applications
ACP's concrete deployment was IBM's BeeAI platform, where it served as the reference implementation for agent-to-agent coordination. Because ACP merged into A2A only months after launch, it never accumulated broad independent production use — a fact worth stating plainly rather than papering over with invented use cases. BeeAI itself continued, but transitioned to A2A: its agents became A2A-compliant through adapters (an A2AServer to expose BeeAI agents, an A2AAgent to consume external ones), so the platform now interoperates with agents from any framework rather than only ACP-native ones.
The practical takeaway for anyone building today is that ACP has no greenfield application. Its lasting contribution is historical and architectural: it validated the manifest-and-REST approach to agent coordination, and its team folded that expertise into A2A.
Challenges
The defining challenge for ACP was not technical but ecological — the risk of standards fragmentation.
- Two standards for one problem. ACP and A2A launched roughly a month apart (ACP in March 2025, A2A in April), both aiming to standardize agent-to-agent communication, both eventually under the Linux Foundation. Two competing standards for the same layer fragment adoption and force developers to pick sides. The resolution — merging ACP into A2A in August 2025 — was the healthier outcome, but it left ACP as a short-lived specification.
- Migration debt. Anyone who adopted ACP early inherited a migration to A2A. The Linux Foundation published migration paths and BeeAI shipped adapters, but the episode is a reminder that building on a brand-new protocol before the ecosystem consolidates carries real switching cost.
- An overloaded name. "ACP" also denotes the unrelated Agentic Commerce Protocol in the payments world, so the acronym alone is ambiguous — a small but real source of confusion when reading agent-protocol documentation.