---
title: "MessagesFallbackParam"
---

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


## Fields

| Field                          | Type                           | Required                       | Description                    | Example                        |
| ------------------------------ | ------------------------------ | ------------------------------ | ------------------------------ | ------------------------------ |
| `model`                        | *str*                          | :heavy_check_mark:             | N/A                            |                                |
| `__pydantic_extra__`           | Dict[str, *Nullable[Any]*]     | :heavy_minus_sign:             | N/A                            | \{<br/>"model": "claude-opus-4-8"<br/>} |