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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.

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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.

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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.

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Configuration

{
  "model": "openrouter/fusion",
  "plugins": [
    {
      "id": "fusion",
      "analysis_models": [
        "~anthropic/claude-opus-latest",
        "~openai/gpt-latest",
        "~google/gemini-pro-latest"
      ],
      "model": "~openai/gpt-latest"
    }
  ]
}
FieldDefaultDescription
presetnoneA curated OpenRouter preset slug (e.g. general-high) that expands into a panel + judge, so you don’t have to name models. Explicit analysis_models / model override it. See Presets.
analysis_modelsQuality preset (~anthropic/claude-opus-latest, ~openai/gpt-latest, ~google/gemini-pro-latest)Models that form the panel. Each runs in parallel with openrouter:web_search and openrouter:web_fetch. 1–8 models allowed.
modelFirst model in the Quality preset (~anthropic/claude-opus-latest)The judge model that produces the structured analysis. With model: "openrouter/fusion", this also becomes the model that writes your final answer; when you attach the plugin to your own model instead, the judge defaults to that model.
max_tool_calls8Max tool-calling steps each panel model and the judge may take in their openrouter:web_search / openrouter:web_fetch loop before they must return text. Range 1–16.
enabledtrueSet to false to bypass fusion for a single request.
When you send model: "openrouter/fusion" without a plugin config, the defaults match the Quality preset on the Fusion lab.

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Presets

Don’t want to pick models? Reference a curated preset by slug with preset — the panel and judge are chosen for you: 
{
  "model": "openrouter/fusion",
  "plugins": [{ "id": "fusion", "preset": "general-budget" }]
}
Slugs follow <task>-<tier>: task is what you’re optimizing the panel for, and tier is the quality/cost/speed tradeoff (high = strongest models, budget = cheaper panel with the same frontier judge, fast = a latency-homogeneous panel where every model has similar TTFT so no single model gates the fan-out). These mirror the presets shown in the Fusion lab UI.
PresetFor
general-highThe strongest all-round panel.
general-budgetA cheaper panel with a frontier judge for strong synthesis at lower cost.
general-fastA latency-homogeneous panel optimized for fast agentic turns, with a frontier judge.
Explicit analysis_models or model always take precedence over a preset.

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Two entry points, one pipeline

openrouter/fusion is equivalent to enabling the openrouter:fusion server tool on the configured model. These behave identically: 
{
  "model": "openrouter/fusion",
  "messages": [
    { "role": "user", "content": "What are the strongest arguments for and against carbon taxes?" }
  ]
}
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.

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Complete example

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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.