Short answer
UHP, the Unified Harness Protocol, is the open standard for the configured-harness boundary: how a product discovers, configures, selects, and drives an agent harness, including tasks, sessions, streaming, files, and cancellation. MHS, the Model Hardware Standard, is Anthropic's specification for reaching programmable physical devices: discovery, read and write primitives, a per-device reference file, and safety limits that live in the driver. They sit on opposite sides of the harness and do not compete. A harness reaches MHS devices through MCP, a command line, or code, while a product drives that harness through UHP. As of 2026-09-13, UHP is an open standard with a versioned specification dated 2026-08-11 and a conformance suite; MHS is a limited Anthropic research preview with access on application and open sourcing planned but not yet published.
- UHP connects a product to an agent harness; MHS connects agents to physical devices such as lab instruments and robots. Different boundaries, with no overlap in their published scopes.
- Status differs sharply: UHP is an open standard with a versioned specification, reference implementation, conformance suite, and one independent client implementation. MHS is a research preview announced 2026-08-27, with access on application and open sourcing planned.
- They compose through the harness: a product starts and follows the task over UHP, and the harness reaches MHS-described devices through MCP, a CLI, or code. Facts verified 2026-09-13.
Two standards on opposite sides of the harness
The agent stack has boundaries above and below the harness, and UHP and MHS take one each. UHP, the Unified Harness Protocol, is an open standard initiated by HarnessRouter for the configured-harness boundary: how a product discovers, configures, selects, and drives a harness, with tasks, sessions, streaming, files, and cancellation. MHS, the Model Hardware Standard, was announced by Anthropic on 2026-08-27, developed with HHMI Janelia Research Campus, as a research preview of a driver standard for programmable physical equipment: microscopes, liquid handlers, robotic arms. An agent reaches an MHS device through MCP, a command-line interface, or code, which places MHS below the harness, on the device side, while UHP sits above it, on the product side. No official MHS material describes a relationship to UHP; the layering here follows each project's own published description. Facts verified 2026-09-13.
The questions each standard answers
These are answers to different questions at different layers, not competing answers to one question.
- What it connects
- UHP connects a product to an agent harness through one unified interface: the product selects a harness, configures its model, skills, MCP servers, and available tools, and drives it. MHS connects agents to physical devices, each described by a reference file the agent can read before it acts.
- What it carries
- UHP carries harness configurations and lifecycle operations, plus tasks, sessions, streamed events, files, and cancellation. MHS carries device discovery, read and write primitives, and per-device descriptions with safety limits enforced in the driver.
- Where limits live
- Under UHP, limits live in the harness configuration the product selects, such as tool restrictions. Under MHS, device-level safety limits live in the driver rather than in the model's instructions.
UHP and MHS, boundary by boundary
This maps each standard's boundary and status; it is not a feature or maturity scorecard. Facts as of 2026-09-13.
| Dimension | UHP | MHS |
|---|---|---|
| Primary boundary | Product to a configured agent harness | Agent to programmable physical devices |
| Initiated by | HarnessRouter, and adopted independently | Anthropic, developed with HHMI Janelia Research Campus |
| Unit of exchange | A task, with its session, streamed events, and files | Device discovery plus reads and writes, guided by a per-device reference file |
| How it is reached | HTTP and Server-Sent Events from the product | Through MCP, a command-line interface, or code, from the agent side |
| Status | Open standard: versioned specification dated 2026-08-11, reference implementation, conformance suite, one independent client implementation | Research preview announced 2026-08-27: access on application, open sourcing planned but not yet published |
When each standard is the one you reach for
- You are building a product on agents
- That is UHP's layer: configure the harness, start tasks, stream progress, continue sessions, and collect files, the same way across harnesses.
- You are connecting agents to instruments or machines
- That is MHS's layer, reached from the harness through MCP, a CLI, or code. As of 2026-09-13 it is a research preview with access on application, so plan for an application process rather than a public spec.
- You are doing both
- The standards compose through the harness: the product drives the harness over UHP, and the harness operates MHS-described devices within the limits their drivers enforce. One system can speak both without either replacing the other.
FAQ
- Do UHP and MHS compete?
- No. They standardize different boundaries: UHP is the product-to-harness interface, and MHS is the agent-to-device interface. A system can use both at once, with the harness in the middle.
- Is MHS an open standard like UHP?
- Not yet. As of 2026-09-13, MHS is a limited Anthropic research preview: reading or implementing it requires an access application, and Anthropic says it plans to open source the specification after safety evaluations. UHP is already an open standard with a public versioned specification, a reference implementation, and a conformance suite.
- Can one product use UHP and MHS together?
- Yes, in the layered sense: the product configures and drives a harness through UHP, and the harness reaches MHS-described devices through MCP, a command-line interface, or code. No official MHS material defines a direct MHS-to-UHP interface, and none is needed for the two to compose.
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