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

# MessagesFallbackParam

Fallback model to try when the primary model fails or refuses. Only the `model` field is supported; per-attempt overrides are rejected.

## Example Usage

```typescript theme={null}
import { MessagesFallbackParam } from "@openrouter/sdk/models";

let value: MessagesFallbackParam = {
  model: "claude-opus-4-8",
};
```

## Fields

| Field                  | Type                   | Required             | Description | Example                                   |
| ---------------------- | ---------------------- | -------------------- | ----------- | ----------------------------------------- |
| `model`                | *string*               | :heavy\_check\_mark: | N/A         |                                           |
| `additionalProperties` | Record\<string, *any*> | :heavy\_minus\_sign: | N/A         | \{<br />"model": "claude-opus-4-8"<br />} |