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FeaturesTTS Vendor Settings

Google

Gemini TTS controls for Google TTS.

Google tuning is passed in synthesizer.options.

{
  "verb": "say",
  "text": "Thanks for calling, how can I help you today?",
  "synthesizer": {
    "vendor": "google",
    "language": "en-US",
    "voice": "your-gemini-voice-name",
    "options": {
      "model": "gemini-2.5-flash-preview-tts",
      "prompt": "Say this in a warm, friendly tone."
    }
  }
}

Options

Gemini TTS

model
string

The model to use. When set, this enables Gemini TTS. Example: gemini-2.5-flash-preview-tts.

apiMode
string

Which Google TTS API to use: tts (standard Cloud TTS voices), live (HD voices in streaming mode) or gemini (Gemini TTS). When omitted it is chosen for you: gemini if a model is set on the verb or credential, live for an HD voice, otherwise tts.

prompt
string

Guidance on tone, emotion or speaking style for the generated speech. Gemini TTS only.

These options apply to the say verb. Google TTS used by an agent over the streaming path uses only the voice and language.

Streaming

Google supports TTS streaming.