Short answer
UHP and A2A standardize different relationships. UHP defines how a product drives a complete agent harness as infrastructure. A2A defines how independent agentic systems discover capabilities, exchange messages, delegate work and track collaborative tasks across an interoperability boundary.
The diagram is conceptual. UHP does not require MCP or A2A, and A2A does not require UHP. The protocols can be composed because they operate at different boundaries.
UHP vs A2A
| Question | UHP | A2A |
|---|---|---|
| Primary boundary | Product/client ↔ complete agent harness runtime | A2A client/agent ↔ independent remote agentic system |
| Main goal | Execute and control harness work consistently | Agent discovery, communication, delegation and collaboration |
| Typical unit of work | Harness task/response with sessions, progress and files | Messages and Tasks that can produce Artifacts |
| Discovery | Harness/capability discovery inside the UHP server contract | Agent Cards describe remote agent identity, interfaces, capabilities and skills |
| Long-running work | Task lifecycle, streaming, continuation and cancellation | Task states with polling, streaming and push-notification patterns |
| Current version checked | 2026-08-11 · Draft standard | v1.0 · stable production-ready line in current official documentation |
| Governance context | Initiated and led by HarnessRouter | Open-source project under the Linux Foundation with a multi-company technical steering committee |
When you might use both
Consider an application that lets a user choose a coding harness and then asks that running harness to delegate a specialized task to a remote research agent. UHP can normalize how the application starts and controls the harness. A2A can normalize how that harness or its surrounding agent system communicates with the remote agent.
Why A2A is a useful comparison for UHP
Searches for “agent interoperability” often collapse several layers into one. MCP standardizes tool/context access, A2A standardizes agent-to-agent interoperability, and UHP targets harness execution. Comparing the boundaries is more useful than asking which single protocol “wins.”
Common mistakes
- “UHP replaces A2A.” No; they solve different interoperability problems.
- “A2A is a harness API.” Its core model is remote agent interoperability, not selecting and operating local or hosted harness runtimes as a shared execution layer.
- “One stack must use all three protocols.” No. Use only the boundaries your system needs.