March 12, 2026 | Synthflow

Fallback Voice Provider Support

We have updated our Public API to support fallback voice configurations. These changes allow you to specify a secondary voice provider and model to be used in case the primary synthesizer fails.

API Changes

The assistants API has been updated to include fallback voice fields within the agent object for GET, POST, and PUT requests.

Field	Type	Description
`fallback_voice_id`	`string`	The ID of the fallback voice.
`fallback_provider`	`string`	The provider for the fallback voice (e.g., `elevenlabs`, `deepgram`, `azure`).
`fallback_model`	`string`	The model to be used by the fallback provider.

Example usage:

1 {
2   "name": "My Assistant",
3   "agent": {
4     "prompt": "You are a helpful assistant.",
5     "voice_id": "primary_voice_id",
6     "provider": "elevenlabs",
7     "fallback_voice_id": "fallback_voice_id",
8     "fallback_provider": "deepgram",
9     "fallback_model": "aura-asteria-en"
10   }
11 }

Updated endpoints:

Endpoint	Title
GET /assistants	List agents
GET /assistants/{model_id}	Get an agent
POST /assistants	Create an agent
PUT /assistants/{model_id}	Update an agent