Model Fallback Input • AI Agent SDK

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

ModelFallbackInput

Defined in the events module.

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.

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