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Overview

GoModel exposes failover through the fallback config block. When a request fails, GoModel can retry it against alternate models. For predictable behavior, use manual mode.

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Manual Mode

Manual mode is the recommended mode today. 
fallback:
  default_mode: "manual"
  manual_rules_path: "config/fallback.json"
config/fallback.json is a JSON object where each model entry contains an ordered candidate list (array); top-level keys are not ordered: 
{
  "gpt-4o": [
    "azure/gpt-4o",
    "gemini/gemini-2.5-pro"
  ]
}
The order-sensitive part is the array under each model entry. GoModel tries the listed candidates in order and stops on the first success. Use bare model names like gpt-4o or provider-qualified selectors like azure/gpt-4o. If needed, you can override the mode per model with fallback.overrides.

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Auto Mode

auto mode is experimental right now.
fallback:
  default_mode: "auto"
  manual_rules_path: "config/fallback.json"
Auto mode keeps any manual candidates first, then appends up to five extra candidates from the current model registry. It prefers models with the same request category, similar rankings, overlapping capabilities, and the same family when possible.

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When It Runs

Failover is attempted only after the primary request returns:
  • 5xx
  • 429
  • model unavailable, unsupported, or not found style errors
It currently applies to translated /v1/chat/completions and /v1/responses requests, not /v1/embeddings.