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

# Model Fallback Input • AI Agent SDK

> ModelFallbackInput: Input for MODEL_FALLBACK hooks (primary model unavailable mid-turn).

# ModelFallbackInput

> Defined in the [**events**](https://praison.ai/docs/sdk/reference/praisonaiagents/modules/events.md) module.

AI Agent

Input for MODEL\_FALLBACK hooks (primary model unavailable mid-turn).

Fired by the agent's LLM recovery loop at the exact point it swaps the
primary model for the next entry in the configured `fallback_models`
chain, so an otherwise silent quality/cost degradation becomes an
observable state transition (Issue #3820). Notification only: the turn
continues on `to_model`. Only the failure class is exposed
(`reason_category`) — provider internals stay redacted, mirroring the
redaction discipline of the other error-path events.

## Properties

**from\_model** `str`

No description available.

**to\_model** `str`

No description available.

**reason\_category** `str`

No description available.

**fallback\_index** `int`

No description available.

> [accordion] Internal & Generic Methods
>
> * **to\_dict**: Generic utility method.

## Source

> [card] [View on GitHub](https://github.com/MervinPraison/PraisonAI/blob/main/src/praisonai-agents/praisonaiagents/hooks/events.py#L216)
>
> `praisonaiagents/hooks/events.py` at line 216


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