> ## Documentation Index
> Fetch the complete documentation index at: https://docs.inworld.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Extra Body Parameters

> Control model selection and fallbacks with extra_body parameters

## Overview

The `extra_body` parameter allows you to fine-tune model selection, fallbacks, and optimization preferences. All parameters are optional.

## Parameters

### `models`

An array of model identifiers to consider for selection or use as fallbacks.

**For specific model requests**: These are used as fallback models if the primary model fails.

**For auto model selection**: These define the pool of models to choose from.

```json theme={"system"}
{
  "extra_body": {
    "models": [
      "anthropic/claude-opus-4-6",
      "google-ai-studio/gemini-2.5-pro",
      "openai/gpt-5"
    ]
  }
}
```

### `ignore`

An array of providers or specific models to exclude from selection or fallbacks.

You can exclude:

* **Entire providers**: `"groq"` excludes all Groq models
* **Specific models**: `"groq/llama-3.3-70b-versatile"` excludes only that model

```json theme={"system"}
{
  "extra_body": {
    "ignore": [
      "groq",                              // Exclude all Groq models
      "groq/llama-3.3-70b-versatile"      // Exclude specific model
    ]
  }
}
```

### `sort`

An array of sorting criteria in priority order. The optimizer uses these to rank and select models.

Available criteria:

* `"price"` - Cost optimization
* `"latency"` - Low latency
* `"throughput"` - High throughput
* `"intelligence"` - General intelligence/capability
* `"math"` - Mathematical reasoning
* `"coding"` - Code generation and understanding

```json theme={"system"}
{
  "extra_body": {
    "sort": [
      "coding",      // Prioritize coding-optimized models
      "price",       // Then consider cost
      "latency"      // Finally optimize for speed
    ]
  }
}
```

<Note>
  **Format Difference**: The `sort` field in `extra_body` (for chat completions) uses string arrays like `["price", "latency"]`. However, when using `sort` in router configuration within `model_selection`, you must use object array format: `[{"metric": "SORT_METRIC_PRICE"}, {"metric": "SORT_METRIC_LATENCY"}]`. See [Create Router](/api-reference/routerAPI/routerservice/create-router#model-selection-in-variants) for router configuration details.
</Note>

### `provider`

An object that controls provider-level routing when the model is specified without a provider prefix (e.g., `"model": "gpt-oss-120b"`).

| Field             | Type       | Default | Description                                                                  |
| :---------------- | :--------- | :------ | :--------------------------------------------------------------------------- |
| `order`           | `string[]` | —       | Explicit list of providers to try, in order (e.g., `["groq", "fireworks"]`). |
| `allow_fallbacks` | `boolean`  | `true`  | Whether to fall back to the next provider if the current one fails.          |

```json theme={"system"}
{
  "extra_body": {
    "provider": {
      "order": ["groq", "fireworks"],
      "allow_fallbacks": true
    }
  }
}
```

When no `order` is specified, the `sort` criteria determines the order providers are tried. If no `sort` is specified either, providers are selected by lowest latency.

When `order` is specified, providers are tried in the listed order — `sort` does not reorder the provider list, but still applies to `models` fallbacks.

See [Provider Routing](/router/usage/specific-model#provider-routing) for detailed examples and execution order.

### `metadata`

An object containing key-value pairs that can be used for conditional routing with CEL expressions. This is used when routing with Routers that have conditional routes.

```json theme={"system"}
{
  "extra_body": {
    "metadata": {
      "tier": "premium",
      "user_id": "user-123",
      "region": "us-east",
      "domain": "coding",
      "priority": 8
    }
  }
}
```

The metadata values are evaluated by CEL expressions in your router configuration. For example, a route with `"cel_expression": "tier == \"premium\""` will match when `metadata.tier` is `"premium"`.

See [Conditional Routing](/router/capabilities/conditional-routing) for more details on using metadata for routing.

## Complete Example

```json theme={"system"}
{
  "model": "auto",
  "messages": [{"role": "user", "content": "Write a Python function"}],
  "extra_body": {
    "models": [
      "openai/gpt-5",
      "anthropic/claude-opus-4-6",
      "google-ai-studio/gemini-2.5-pro"
    ],
    "ignore": ["groq"],
    "sort": ["coding", "price", "latency"]
  }
}
```

This configuration:

1. Considers only the three specified models
2. Excludes all Groq models
3. Prioritizes coding capability, then cost, then latency

## Best Practices

* **Be specific with `models`**: Limiting the model pool improves selection speed and predictability
* **Use `ignore` strategically**: Exclude providers or models that don't meet your requirements
* **Order `sort` by priority**: List the most important criteria first
* **Combine criteria**: Use multiple sort criteria for balanced optimization