Short answer
Use a model router for model access. Use HarnessRouter when your product needs an agent harness to return work that a human can review, accept, save, or ship.
- OpenRouter, TokenRouter, and model routers sit near the inference/provider layer.
- HarnessRouter sits between the product UI and a harness run.
- They are complementary; do not position HarnessRouter as a drop-in model gateway.
Give each layer one job
- Product UI
- Collects the user's task, shows run status, and lets the user review the result.
- HarnessRouter
- Routes the product task to the right harness and returns a run your app can handle.
- Agent harness
- Executes the task in a specialized agent environment such as Codex, Claude Code, Hermes, or Pi.
- Model router
- Selects or accesses models, providers, fallback paths, or gateway controls.
The difference is what comes back
| Question | Model router / LLM gateway | HarnessRouter |
|---|---|---|
| Input | Prompt, message, model name, provider preference, or inference request. | Product task that should become completed work inside the app. |
| Output | Model response, JSON, tool-call data, media, embedding, or stream. | Harness run result your product can inspect, render, accept, save, or ship. |
| Best for | Provider access, fallback, cost control, and model choice. | Agent-backed product features without building the harness backend. |
Use both when the product needs both layers
- Keep OpenRouter, TokenRouter, or another model router below the harness/model layer.
- Use HarnessRouter for user-facing work requests that need a harness run.
- Keep the UI language focused on the user's task, not the infrastructure stack.
FAQ
- Is HarnessRouter an OpenRouter alternative?
- No. OpenRouter focuses on model access and routing. HarnessRouter focuses on routing product tasks to agent harnesses.
- Is HarnessRouter a TokenRouter alternative?
- No. TokenRouter-style products belong near the model gateway layer. HarnessRouter belongs near the product workflow and harness run layer.
- Can a product use both?
- Yes. A product can use a model router underneath while HarnessRouter routes the user-facing agent task.