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AssistantsModel configurations

Model fallback configuration

Configure a backup language model that activates automatically if your primary model fails

Model fallback lets a backup language model take over automatically if your primary model fails, so the call can keep going. You can configure fallback models for the OpenAI and Anthropic Bedrock providers. Vapi models fall back automatically, so you don’t configure fallback models for them.

How it works

When a model failure occurs, Vapi will:

  1. Detect the failure of the primary model.
  2. If fallbackModels is configured, choose a fallback model.

Fallback models stay on the same provider as your primary model. To protect against a provider-wide outage, pair model fallback with voice fallback and transcriber fallback on the other two pipeline components, which do support cross-provider fallback.

Configure via Dashboard

You can configure a fallback model for Anthropic Bedrock in the Dashboard. To configure OpenAI fallback models, use the API.

1

Open the assistant

Open the Dashboard. Select Assistants, then select an assistant.

2

Open the model settings

Select the Model card, then choose an Anthropic Bedrock model.

3

Add a fallback model

Expand Advanced. Under Fallback model, select Add fallback model, then choose a model.

Configure via API

Add the fallbackModels field directly to your assistant’s model object, next to model.model. Models don’t use a fallbackPlan wrapper like voice.fallbackPlan.voices and transcriber.fallbackPlan.transcribers.

OpenAI

Set model.fallbackModels to an array of OpenAI model IDs. If the primary model fails, these models are tried, starting with the one expected to respond fastest. Configured fallback models might not be enabled for every account. See fallbackModels for OpenAI in the API reference.

{
  "model": {
    "provider": "openai",
    "model": "gpt-5.5",
    "fallbackModels": ["gpt-5.4", "gpt-4.1"]
  }
}

Most assistants don’t need fallbackModels. The fastest fallback models that suit your primary model are found automatically.

Anthropic Bedrock

Set model.fallbackModels to an array with one Claude model ID available through Bedrock. Bedrock accepts at most one fallback model. See fallbackModels for Anthropic Bedrock in the API reference.

{
  "model": {
    "provider": "anthropic-bedrock",
    "model": "claude-sonnet-4-6",
    "fallbackModels": ["claude-haiku-4-5-20251001"]
  }
}

Verify the configuration

Retrieve the assistant with Get Assistant and confirm that model.fallbackModels lists your fallback models.

FAQ

Not yet. fallbackModels only lets you specify backup models from the same provider as your primary model. Use voice fallback and transcriber fallback to protect those two pipeline components against a provider-wide outage.

Each model is billed at its normal rate. If the primary model uses tokens before it fails, that usage can be included in the call’s cost along with the fallback model’s usage.

fallbackModels is currently only available on OpenAIModel and AnthropicBedrockModel.

No. GPT-Live doesn’t support model fallbacks, and a GPT-Live model can’t be a fallback model. See GPT-Live configuration.

Voice fallback configuration

Configure fallback voices that activate automatically when your primary voice provider fails.

Transcriber fallback configuration

Configure fallback transcribers so calls keep working if your primary speech-to-text provider fails.

Model providers

Compare every language model provider Vapi supports.