A structured comparison of the emerging protocol stack by scope, actors, boundaries, and runtime role.
The goal is not to force false equivalence. It is to show which protocols solve adjacent problems and where the unresolved layer begins.
| Protocol | Primary role | Main actors | What it helps solve | What remains underspecified |
|---|---|---|---|---|
| MCP | Tool and context access | AI app, model, tool, external system | Connects models and applications to tools and data sources | Cross-domain execution semantics, policy-aware routing, governed fallback |
| A2A | Agent collaboration | Agent to agent | Supports communication and coordination across agents | Locality policy, execution-domain semantics, shared fallback contracts |
| ACP | Editor-agent surface | IDE/editor, coding agent | Standardizes editor-facing agent communication | General hybrid execution semantics across distributed environments |
| HAINP | Hybrid execution and governance | Nodes, agents, runtimes, policy layers | Defines execution domains, locality, routing, fallback, portability, and audit continuity | Does not replace transport, tool access, or generic agent collaboration layers |
Protocols do not need to be mutually exclusive to be strategically important. HAINPRO assumes composition by layer, not winner-takes-all replacement.