Voice Fallback Plan

Introduction

By default, if an assistant’s primary voice experiences any failure, Vapi will automatically attempt to use other available voices to continue the call. While this ensures call continuity, you might want more control over which specific voices are used as fallbacks.

Fallback plans give you precise control over the fallback sequence. Your assistant will sequentially fallback to only the voices you configure within your plan, in the exact order you specify.

How It Works

When a voice failure occurs, Vapi will:

1. Detect the failure of the primary voice
2. If a custom fallback plan exists:

• Switch to the first fallback voice in your plan
• Continue through your specified list if subsequent failures occur
• Terminate only if all voices in your plan have failed

3. If no custom fallback plan is configured:

• Automatically switch to other available voices
• Continue attempting different voices
• Terminate only if all available voices have failed

Configuration

Add the fallbackPlan property to your assistant’s voice configuration, and specify the fallback voices within the voices property.

• Please note that fallback voices must be valid JSON configurations, and not strings.
• The order matters. Vapi will choose fallback voices starting from the beginning of the list.

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{
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  "voice": {
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    "provider": "openai",
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    "voiceId": "shimmer",
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    "fallbackPlan": {
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        "voices": [
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            {
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                "provider": "cartesia",
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                "voiceId": "248be419-c632-4f23-adf1-5324ed7dbf1d"
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            },
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            {
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                "provider": "playht",
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                "voiceId": "jennifer"
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            }
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        ]
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    }
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  }
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}

Although not recommended, you may choose to disable the default fallback behavior by providing an empty list of voices in your fallback plan:

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{
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  "voice": {
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    "provider": "openai",
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    "voiceId": "shimmer",
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    "fallbackPlan": {
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        "voices": []
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    }
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  }
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}

Best practices

• Use different providers for your fallback voices to protect against provider-wide outages.
• Select voices with similar characteristics (tone, accent, gender) to maintain consistency in the user experience.

How will pricing work?

There is no change to the pricing of the voices. Your call will not incur any extra fees while using fallback voices, and you will be able to see the cost for each voice in your end-of-call report.