TTS Models

By default Deepgram Text-to-Speech will be used with the Voice Agent API. Deepgram supports two text-to-speech model families, and the agent picks the right TTS endpoint based on the version field of agent.speak.provider — you do not manage endpoint URLs yourself.

Flux TTS (v2) for streaming-first, voice-agent-first synthesis with turn-based lifecycle and cross-turn voice consistency.
Aura (v1) for the broadest Deepgram voice catalog across English and Spanish, and for compressed or containerized output formats.

You can also use Deepgram's native Cartesia support or opt to use another provider's TTS model with your Agent by applying the following settings.

Deepgram TTS models

Deepgram offers two TTS model families for the Voice Agent API. Set agent.speak.provider.version to v2 for Flux TTS or v1 for Aura; within a provider you supply, version defaults to v1. A Settings message that omits agent.speak altogether gets Flux TTS with the flux-kit-en voice.

Choosing a model family

	Flux TTS (V2)	Aura (V1)
Best for	streaming-first voice agents	broadest voice catalog, compressed audio
Turn-based lifecycle	yes	no
Cross-turn voice consistency	yes	no
`provider.version`	`v2` (required)	`v1` (default)
Model string	`flux-{voice}-{language}` (e.g. `flux-alexis-en`)	`aura-2-thalia-en`, `aura-asteria-en`, etc.

Flux TTS

Flux TTS is Deepgram's streaming-first, voice-agent-first text-to-speech model family. It brings a turn-based lifecycle and cross-turn voice consistency built for the realities of a voice agent pipeline. For details, see the Flux TTS Feature Overview.

Parameter	Type	Description
`agent.speak.provider.type`	String	Must be `deepgram`
`agent.speak.provider.version`	String	Must be `v2`
`agent.speak.provider.model`	String	Flux TTS model id in the format `flux-{voice}-{language}`, for example `flux-alexis-en`. See the Flux TTS voice catalog for the full list.
`agent.speak.provider.speed`	Float	Speaking rate multiplier. Accepts `0.5` to `1.5` in `0.05` increments. Defaults to `1.0`.
`agent.speak.provider.expressivity`	Integer	Delivery register on a calm to animated axis, available on every Flux voice. Accepts `-2`, `-1`, `0`, `1`, or `2`. Defaults to `0`, the voice's tuned delivery. Beta — see Expressivity.

Example

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{
  "agent": {
    "speak": {
      "provider": {
        "type": "deepgram",
        "version": "v2",
        "model": "flux-alexis-en",
        "speed": 1.05
      }
    }
  }
}

Audio output formats

Flux TTS streams raw audio frames, so it accepts a narrower set of audio.output settings than Aura:

Setting	Accepted with Flux TTS
`encoding`	`linear16`, `mulaw`, `alaw`
`container`	`none`
`sample_rate`	`8000`, `16000`, `24000`, `32000`, `44100` or `48000` for `linear16` (default `24000`); `8000` or `16000` for `mulaw` and `alaw` (default `8000`)
`bitrate`	not accepted

Requesting a compressed encoding (mp3, opus, flac, aac) or a container such as wav returns INVALID_SETTINGS. Configure an Aura voice to use those formats.

Aura

For a complete list of Deepgram Aura TTS models see TTS Voice Selection.

Parameter	Type	Description
`agent.speak.provider.type`	String	Must be `deepgram`
`agent.speak.provider.version`	String	Optional. Defaults to `v1` when omitted.
`agent.speak.provider.model`	String	The Aura TTS model to use, for example `aura-2-thalia-en`.
`agent.speak.provider.speed`	Float	Speaking rate multiplier. Range: `0.7` - `1.5`. Defaults to `1.0`. See TTS voice controls for details.

Example

JSON

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{
  "speak": {
    "provider": {
      "type": "deepgram",
      "model": "aura-2-thalia-en",
      "speed": 0.9
    }
  }
}

Deepgram-managed Cartesia TTS models

Deepgram also provides managed support for Cartesia TTS. For a complete list of Cartesia TTS models, visit Cartesia's TTS Docs. Cartesia is included in the Standard pricing tier.

Parameter	Type	Description
`agent.speak.provider.type`	String	Must be `cartesia`
`agent.speak.provider.model`	String	The TTS model to use
`agent.speak.provider.speed`	String or Number	Speaking rate control. Accepts `slowest`, `slow`, `normal`, `fast`, `fastest`, or a numerical value for more granular control. See Cartesia speed documentation.

Example

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{
"agent": {
  "speak": {
    "provider": {
      "type": "cartesia",
      "model_id": "sonic-2",
      "voice": {
        "mode": "id",
        "id": "a167e0f3-df7e-4d52-a9c3-f949145efdab"
      },
      "speed": "normal"
    }
  }
}
}

BYO Third Party TTS models

To use a third party TTS voice, specify the TTS provider and required parameters.

OpenAI

For OpenAI you can refer to OpenAI's text-to-speech guide on how to find your voice ID.

Parameter	Type	Description
`agent.speak.provider.type`	String	Must be `open_ai`
`agent.speak.provider.model`	String	The TTS model to use
`agent.speak.provider.voice`	String	The voice to use
`agent.speak.endpoint`	Object	Required and must include url and headers
`agent.speak.endpoint.url`	String	Your OpenAI API endpoint URL
`agent.speak.endpoint.headers`	Object	Required headers for authentication

Example

JSON

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{
  "agent": {
    "speak": {
      "provider": {
        "type": "open_ai",
        "model": "tts-1",
        "voice": "alloy"
      },
      "endpoint": {
        "url": "https://api.openai.com/v1/audio/speech",
        "headers": {
          "authorization": "Bearer {{OPENAI_API_KEY}}"
        }
      }
    }
  }
}

Eleven Labs

For ElevenLabs you can refer to this article on how to find your Voice ID or use their API to retrieve it. See their TTS Docs for more information. ElevenLabs does not support WebSocket streaming for the eleven_v3 model - instead, use the HTTPS REST endpoint (see example).

Parameter	Type	Description
`agent.speak.provider.type`	String	Must be `eleven_labs`
`agent.speak.provider.model_id`	String	The model ID to use
`agent.speak.provider.language_code`	String	Optional Language code
`agent.speak.endpoint`	Object	Must include url and headers
`agent.speak.endpoint.url`	String	Your Eleven Labs API endpoint URL
`agent.speak.endpoint.headers`	Object	Headers for authentication

Example

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{
  "agent": {
    "speak": {
      "provider": {
        "type": "eleven_labs",
        "model_id": "eleven_turbo_v2_5",
        "language_code": "en-US"
      },
      "endpoint": {
        "url": "wss://api.elevenlabs.io/v1/text-to-speech/{voice_id}/multi-stream-input",
        "headers": {
          "xi-api-key": "{{ELEVEN_LABS_API_KEY}}"
        }
      }
    }
  }
}

Example (eleven_v3 via HTTPS)

Because eleven_v3 does not support WebSocket streaming, use the HTTPS REST endpoint:

JSON

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{
  "agent": {
    "speak": {
      "provider": {
        "type": "eleven_labs",
        "model_id": "eleven_v3",
        "language_code": "en-US"
      },
      "endpoint": {
        "url": "https://api.elevenlabs.io/v1/text-to-speech/{voice_id}",
        "headers": {
          "xi-api-key": "{{ELEVEN_LABS_API_KEY}}"
        }
      }
    }
  }
}

Cartesia

For Cartesia you can use their API to retrieve a voice ID. See their TTS API Docs for more information.

Parameter	Type	Description
`agent.speak.provider.type`	String	Must be `cartesia`
`agent.speak.provider.model_id`	String	The model ID to use
`agent.speak.provider.voice`	Object	Cartesia Voice configuration
`agent.speak.provider.voice.mode`	String	The voice mode to use
`agent.speak.provider.voice.id`	String	The voice ID to use
`agent.speak.provider.language`	String	Language setting
`agent.speak.endpoint`	Object	Must include url and headers
`agent.speak.endpoint.url`	String	Your Cartesia API endpoint URL
`agent.speak.endpoint.headers`	Object	Headers for authentication

Example

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{
  "agent": {
    "speak": {
      "provider": {
        "type": "cartesia",
        "model_id": "sonic-2",
        "voice": {
          "mode": "id",
          "id": "a167e0f3-df7e-4d52-a9c3-f949145efdab"
        },
        "language": "en"
      },
      "endpoint": {
        "url": "https://api.cartesia.ai/tts/bytes",
        "headers": {
          "x-api-key": "{{CARTESIA_API_KEY}}"
        }
      }
    }
  }
}

Amazon (AWS) Polly

For Amazon (AWS) Polly you can refer to this article for a list of available voices.

Parameter	Type	Description
`agent.speak.provider.type`	String	Must be `aws_polly`
`agent.speak.provider.language_code`	String	The language code to use
`agent.speak.provider.voice`	String	The voice to use
`agent.speak.provider.engine`	String	The engine to use
`agent.speak.provider.credentials`	Object	The credentials to use

STS Example

JSON

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{
  "agent": {
    "speak": {
      "provider": {
        "type": "aws_polly",
        "language_code": "en-US",
        "voice": "Matthew",
        "engine": "standard",
        "credentials": {
          "type": "sts",
          "region": "us-west-2",
          "access_key_id": "{{AWS_ACCESS_KEY_ID}}",
          "secret_access_key": "{{AWS_SECRET_ACCESS_KEY}}",
          "session_token": "{{AWS_SESSION_TOKEN}}"
        }
      },
      "endpoint": {
        "url": "https://polly.us-west-2.amazonaws.com/v1/speech"
      }
    }
  }
}

IAM Example

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{
  "agent": {
    "speak": {
      "provider": {
        "type": "aws_polly",
        "voice": "Joanna",
        "language_code": "en-US",
        "engine": "standard",
        "credentials": {
          "type": "iam",
          "region": "us-east-2",
          "access_key_id": "{{AWS_ACCESS_KEY_ID}}",
          "secret_access_key": "{{AWS_SECRET_ACCESS_KEY}}"
        }
      },
      "endpoint": {
        "url": "https://polly.us-east-2.amazonaws.com/v1/speech"
      }
    }
  }
}

Using multiple TTS providers

The speak object accepts both a single provider and an array of providers. When you supply an array, the Voice Agent uses the providers as an ordered fallback chain: it sends each TTS request to the first provider in the list and automatically falls back to the next provider if the request fails.

How fallback works

The agent sends the request to the first provider in the array.
If that provider returns an error or times out, the agent sends a SPEAK_REQUEST_FAILED warning over the WebSocket and retries with the next provider.
This continues through every provider in the array.
If all providers fail, the agent sends a FAILED_TO_SPEAK error and the turn produces no audio response.

The fallback is per-request — each new agent utterance starts again from the first provider. Provider order matters, so place your preferred provider first and your most reliable fallback last.

Example

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{
  "agent": {
    "speak": [
      {
        "provider": {
          "type": "deepgram",
          "version": "v2",
          "model": "flux-kit-en"
        }
      },
      {
        "provider": {
          "type": "open_ai",
          "model": "tts-1",
          "voice": "shimmer"
        },
        "endpoint": {
          "url": "https://api.openai.com/v1/audio/speech",
          "headers": {
            "authorization": "Bearer {{OPENAI_API_KEY}}"
          }
        }
      }
    ]
  }
}

Search documentation

Self-Hosted Deployments

TTS Models

Deepgram TTS models

Choosing a model family

Flux TTS

Example

Audio output formats

Aura

Example

Deepgram-managed Cartesia TTS models

Example

BYO Third Party TTS models

OpenAI

Example

Eleven Labs

Example

Example (eleven_v3 via HTTPS)

Cartesia

Example

Amazon (AWS) Polly

STS Example

IAM Example

Using multiple TTS providers

How fallback works

Example

What's Next

Self-Hosted Deployments