Short answer
AG-UI is an open standard for the agent-to-user edge: it streams an agent's messages, state, tool activity, and interaction to a user-facing frontend so an application can render what the agent is doing. UHP, the Unified Harness Protocol, is an open standard for the agent's other edge: connecting an application to the harness that runs the agent, covering tasks, sessions, streaming, files, and cancellation. These are adjacent edges of the same agent application, front-of-house and the harness behind it, and in one topology they compose: an application invokes and controls the harness through a UHP server, and AG-UI streams that run to the user interface. Because both touch the application layer, whether they are strictly separate or partly overlap depends on the architecture. 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.
- AG-UI connects an agent to a user-facing frontend; UHP connects an application to the harness that runs the agent. Adjacent edges of the same app, front and back.
- AG-UI is an open standard for streaming agent activity and state to a UI. UHP is a newer open standard for the application-to-harness boundary, with a versioned specification, reference implementation, conformance suite, and one independent client implementation.
- In one topology they compose: UHP behind, AG-UI in front. Because both touch the application layer, whether they overlap depends on the architecture, not on an inherent rule. Facts verified 2026-08-27.
Front-of-house and the harness behind it
AG-UI and UHP touch adjacent edges of the same agent application, so this page is careful not to overstate a clean separation. AG-UI is an open standard for the agent-to-user edge: it carries an agent's messages, state, tool-call activity, and interaction as events a user-facing frontend can render, so people can watch and steer what an agent is doing. UHP, the Unified Harness Protocol, is an open standard for the agent's other edge: an application invoking and controlling the harness that runs the agent, covering tasks, sessions, streaming, files, and cancellation. One is front-of-house, the connection to the user interface; the other is the connection to the harness behind the application. All facts here are from public materials, verified 2026-08-27.
The questions each open standard answers
Both touch the application layer, so read these as adjacent edges, not a hard split.
- Which edge
- AG-UI: the agent-to-user edge, streaming activity to a frontend. UHP: the application-to-harness edge, invoking the harness that runs the agent.
- Direction of interest
- AG-UI: presenting and steering a run in a user interface. UHP: starting, controlling, and collecting a run from an application.
- What it carries
- AG-UI: messages, state, tool activity, and interaction events for a UI. UHP: tasks, sessions, streaming, files, and cancellation for a run.
AG-UI and UHP, by edge
This maps each open standard's edge; the two are adjacent and can compose, so it is not a clean either-or and not a scorecard. Facts as of 2026-08-27.
| Dimension | AG-UI | UHP |
|---|---|---|
| Primary edge | Agent to user-facing frontend | Application to the harness that runs the agent |
| What it is for | Rendering and steering a run in a user interface | Invoking, controlling, and collecting a run from an application |
| What it carries | Messages, state, tool activity, and interaction events | Tasks, sessions, streaming, files, and cancellation for a run |
| Maturity | Open standard for agent-to-UI streaming, growing ecosystem | Newer open standard; versioned spec, reference implementation, conformance suite, and one independent client implementation |
| How they compose | Streams the run to the user interface | Lets an application invoke and control the harness through a UHP server; AG-UI can stream that run to the UI |
When each open standard is the one you reach for
- You are rendering an agent's activity in a user interface
- That is AG-UI's edge: an open standard for streaming an agent's messages, state, and tool activity to a frontend so users can watch and steer it. UHP does not render a UI.
- You are invoking a harness from an application
- That is UHP's edge: an application invoking and controlling the harness that runs the agent, with tasks, sessions, streaming, files, and cancellation, as an open standard with a versioned specification.
- You are building a full agent app
- For a product that runs agents, UHP is the application-to-harness contract behind your product: your application invokes and controls the harness through a UHP server, and AG-UI streams that run to the interface in front.
FAQ
- Are UHP and AG-UI competitors?
- They touch adjacent edges of the same agent application: AG-UI streams an agent's activity to a user-facing frontend, and UHP connects an application to the harness that runs the agent. In one topology they compose, UHP behind and AG-UI in front; because both touch the application layer, whether they overlap depends on the architecture.
- Can I use UHP and AG-UI together?
- Yes, in a common topology: an application invokes and controls the harness over UHP, and AG-UI streams that run's messages, state, and tool activity to the user interface. They address different edges of the same application.
- 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.