Fusion

The Fusion plugin gives your model access to a multi-model deliberation tool. When the model invokes it, a panel of models answers your prompt in parallel (with openrouter:web_search), a judge compares their responses and returns structured analysis, and your model uses that analysis to write a better final answer.

The Fusion plugin is a configuration surface for the openrouter:fusion server tool. It’s also the mechanism behind the openrouter/fusion model alias. All three entry points hit the same pipeline.

When to use Fusion

Reach for Fusion when a single model isn’t enough — research, expert critique, or tasks that benefit from multiple perspectives. Fusion is overkill for short tactical prompts; use it when the cost of being wrong outweighs the cost of a few extra completions.

How it works

1. The plugin injects the openrouter:fusion tool into your request. If you used model: "openrouter/fusion", it also resolves the alias to a real model.
2. Your model reads the prompt and decides whether to invoke openrouter:fusion.
3. The panel — a set of models — answers your prompt in parallel, each with openrouter:web_search and openrouter:web_fetch enabled.
4. The judge receives all panel responses, with openrouter:web_search and openrouter:web_fetch available, and compares them — it doesn’t merge them. It returns structured analysis as JSON: consensus (points all or most models agree on, treated as higher-confidence), contradictions, partial coverage, unique insights from individual models, and blind spots none of them addressed.
5. Your model receives the structured analysis and writes the final answer.

Configuration

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{
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  "model": "openrouter/fusion",
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  "plugins": [
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    {
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      "id": "fusion",
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      "analysis_models": [
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        "~anthropic/claude-opus-latest",
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        "~openai/gpt-latest",
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        "~google/gemini-pro-latest"
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      ],
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      "model": "~openai/gpt-latest"
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    }
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  ]
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}

When you send model: "openrouter/fusion" without a plugin config, the defaults match the Quality preset on the Fusion lab.

Two entry points, one pipeline

openrouter/fusion is equivalent to enabling the openrouter:fusion server tool on the configured model. These behave identically:

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{
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  "model": "openrouter/fusion",
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  "messages": [
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    { "role": "user", "content": "What are the strongest arguments for and against carbon taxes?" }
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  ]
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}

In both cases, the model decides when to call openrouter:fusion. For prompts that don’t need deliberation, it answers directly — including invoking any other tools you’ve defined.

Complete example

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const response = await fetch('https://dynamicsinfo.com/api/v1/chat/completions', {
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  method: 'POST',
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  headers: {
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    Authorization: 'Bearer {{API_KEY_REF}}',
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    'Content-Type': 'application/json',
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  },
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  body: JSON.stringify({
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    model: 'openrouter/fusion',
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    messages: [
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      {
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        role: 'user',
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        content: 'Compare ridge, lasso, and elastic-net regression. Where does each shine?',
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      },
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    ],
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    plugins: [
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      {
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        id: 'fusion',
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        analysis_models: [
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          '~anthropic/claude-opus-latest',
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          '~openai/gpt-latest',
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        ],
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      },
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    ],
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  }),
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});
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const data = await response.json();
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console.log(data.choices[0].message.content);

Recursion protection

Inner fusion calls carry an x-openrouter-fusion-depth header. Panel and judge models cannot recursively invoke openrouter:fusion — the plugin refuses to inject the tool a second time, keeping deliberation bounded to a single level.

Related

• openrouter:fusion server tool
• Fusion Router (openrouter/fusion)
• Web Search server tool
• Web Fetch server tool
• /labs/fusion — interactive playground