ACP vs MCP: What the Agent Client Protocol Does That MCP Doesn't
ACP (Agent Client Protocol, v1) connects an editor to a coding agent; MCP (spec 2026-07-28) connects an agent to tools. They sit on opposite sides of the agent and are used together: ACP's session/new even carries the MCP servers the agent should start. Here is the feature matrix, the wire flow, and a working agent and client checked against @agentclientprotocol/sdk 2.4.0.