Short answer
A2A, the Agent2Agent protocol, is an established open standard for communication between independent agents: one agent discovers and delegates to another across organizational and framework boundaries. UHP, the Unified Harness Protocol, is an open standard for a different actor and edge: an application invoking and controlling the harness that runs an agent, covering tasks, sessions, streaming, files, and cancellation. Both carry tasks, artifacts, and streaming, so the distinction is not the nouns but who is talking to whom: A2A is agent to agent; UHP is application to harness. They can appear in the same system, and neither replaces the other. UHP is a newer open standard with a versioned specification dated 2026-08-11, a reference implementation, a conformance suite, and one independent client implementation.
- A2A connects agents to other agents; UHP connects an application to the harness that runs an agent. The difference is the actors and the boundary, not the feature list.
- A2A is an established, widely adopted open standard, hosted by the Linux Foundation. UHP is a newer open standard for the application-to-harness layer, with a versioned specification, reference implementation, conformance suite, and one independent client implementation.
- Both can appear in one system: an application invokes a harness over UHP, and agents coordinate with other agents over A2A. Facts verified 2026-08-27.
Same-shaped messages, different actors
A2A and UHP both describe tasks, artifacts, and streaming, which makes a feature-by-feature comparison misleading. What separates them is the actors and the boundary. A2A, the Agent2Agent protocol, is an open standard hosted by the Linux Foundation for communication between independent agents: an agent advertises its capabilities and another agent discovers and delegates work to it, across frameworks and organizations. UHP, the Unified Harness Protocol, is an open standard for the application-to-harness edge: an application invokes and controls a harness that runs an agent, covering tasks, sessions, streaming, files, and cancellation. A2A is agent to agent; UHP is application to harness. All facts here are from public materials, verified 2026-08-27.
The questions each open standard answers
Read these by actor and boundary, not by matching feature nouns.
- Who talks to whom
- A2A: one agent to another independent agent. UHP: an application to the harness that runs an agent.
- The problem it solves
- A2A: discovery and delegation across independent agents and frameworks. UHP: invoking and controlling a harness from an application.
- Where it sits
- A2A: between peer agent systems. UHP: at the application-to-harness boundary beneath an application.
A2A and UHP, by actor and boundary
This maps each open standard's actors and boundary; it is not a feature or maturity scorecard. Facts as of 2026-08-27.
| Dimension | A2A | UHP |
|---|---|---|
| Primary actors | One agent and another independent agent | An application and the harness that runs an agent |
| Primary boundary | Agent to agent, across frameworks and organizations | Application to harness |
| What it carries | Capability discovery, messages, tasks, and artifacts between agents | Tasks, sessions, streaming, files, and cancellation for a run |
| Maturity and governance | Established and widely adopted; hosted by the Linux Foundation | Newer open standard; versioned spec, reference implementation, conformance suite, and one independent client implementation |
| How they compose | Lets an agent delegate to another agent | Lets an application invoke the harness whose agent may then use A2A to reach others |
When each open standard is the one you reach for
- You are connecting independent agents to each other
- That is A2A's layer: an established open standard for discovery and delegation between agents across frameworks and organizations. UHP does not do this job.
- You are invoking a harness from an application
- That is UHP's layer: tasks, sessions, streaming, files, and cancellation across the application-to-harness boundary, as an open standard with a versioned specification.
- You are building a system with both
- For a product that runs agents, UHP is the layer you build on: your application invokes and controls the harness over UHP, and the agent inside it can reach other agents over A2A. The application-to-harness contract is UHP's.
FAQ
- Is UHP a competitor to A2A?
- No. A2A connects independent agents to one another; UHP connects an application to the harness that runs an agent. They describe different actors and boundaries and can appear in the same system.
- A2A and UHP both have tasks and artifacts. Are they the same?
- No. Sharing message shapes does not make them the same: A2A carries them between two independent agents, while UHP carries them across the application-to-harness boundary. The actors and the boundary differ, not just the vocabulary.
- Is UHP an open standard?
- Yes. The Unified Harness Protocol is an open standard. As of 2026-08-27, its public materials include a versioned specification dated 2026-08-11, a reference implementation, and a conformance suite, and the independent adoption tracker lists one independent client implementation, SuperQode. It is newer than A2A and covers a different boundary.