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n. / Cost and performance
Model fallback
Definition
Model fallback is automatically switching to a backup model or provider when the first choice fails, times out or is rate limited, so the user still gets an answer.
In more detail
Fallbacks improve availability but change behavior: a different model may follow instructions differently or cost more. Record which model actually answered on every run, and test the fallback path on purpose, since it is the code that runs least often.
Example
Your primary model returns 429. The agent retries once, then calls a second provider's model. The trace shows both attempts and the model that finally answered.
