> ## Documentation Index > Fetch the complete documentation index at: https://docs.modellix.ai/llms.txt > Use this file to discover all available pages before exploring further. # Gemini 3.8 Flash TTS > [Core Function] Gemini 3.8 Flash TTS is Google's controllable text-to-speech model, currently in Preview. [Strengths] Single-speaker and two-speaker dialogue, preset voices, 130 languages via language_code, and expressive delivery through turn-level style and inline vocal tags. Output is WAV (24 kHz mono PCM). [Best For] Voiceovers, audiobook narration, multilingual speech, podcast-style scripts, and two-person dialogue. [Limitations] Do NOT use this for streaming, voice creation, lip-syncing existing video, music or sound-effect generation, image or audio inputs, MP3/OGG export, or API-level speed, volume, encoding, or sample-rate controls. Dialogue requires exactly two speakers with preset voices. Combined text and style must stay within 8,192 Unicode characters. [Routing] Route here for expressive Gemini TTS with per-turn style control; for the prompt-based request format use Gemini 3.1 Flash TTS; for video with native audio use Veo. ## Billing Billed in **USD per million input characters**. Current prices are listed on the [Modellix Pricing Page](https://www.modellix.ai/pricing). * **Single speaker:** Count Unicode characters in `text`. * **Two speakers:** Sum Unicode characters in all `turns[].text`, without adding separators. * `style`, speaker names, voice names, and `language_code` are excluded from the character count. ## OpenAPI ````yaml /media-model-api/google/google-t2s.json post /google/gemini-3.8-flash-tts openapi: 3.1.0 info: title: Google Text-to-Speech Models API description: >- Google Gemini text-to-speech. Converts plain text into controllable speech audio. Submit an async task, then poll GET /api/v1/tasks/{task_id} for the audio. version: 1.0.0 contact: name: Modellix Support email: support@modellix.ai servers: - url: https://api.modellix.ai/api/v1 description: The text-to-speech models API from Google. security: - bearerAuth: [] paths: /google/gemini-3.8-flash-tts: post: summary: Gemini 3.8 Flash TTS description: >- [Core Function] Gemini 3.8 Flash TTS is Google's controllable text-to-speech model, currently in Preview. [Strengths] Single-speaker and two-speaker dialogue, preset voices, 130 languages via language_code, and expressive delivery through turn-level style and inline vocal tags. Output is WAV (24 kHz mono PCM). [Best For] Voiceovers, audiobook narration, multilingual speech, podcast-style scripts, and two-person dialogue. [Limitations] Do NOT use this for streaming, voice creation, lip-syncing existing video, music or sound-effect generation, image or audio inputs, MP3/OGG export, or API-level speed, volume, encoding, or sample-rate controls. Dialogue requires exactly two speakers with preset voices. Combined text and style must stay within 8,192 Unicode characters. [Routing] Route here for expressive Gemini TTS with per-turn style control; for the prompt-based request format use Gemini 3.1 Flash TTS; for video with native audio use Veo. operationId: gemini38FlashTTSAsync requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/Gemini38FlashTTSRequest' examples: single_speaker: summary: Single speaker with turn style value: text: Have a wonderful day! style: cheerful and friendly language_code: en-us voice: Kore dual_speaker: summary: Two-speaker dialogue, one part per turn value: language_code: en-us speakers: - speaker: Joe voice: Puck - speaker: Jane voice: Kore turns: - speaker: Joe text: How is it going today, Jane? style: cheerful and friendly - speaker: Jane text: Pretty good. Ready when you are. style: calm and relaxed responses: '200': description: >- Task submitted successfully. Poll GET /api/v1/tasks/{task_id} until the task completes; synthesized audio is returned on the task result. content: application/json: schema: $ref: '#/components/schemas/AsyncTaskResponse' example: code: 0 message: success data: status: pending task_id: task-gemini-38-tts-001 model_id: google/gemini-3.8-flash-tts get_result: method: GET url: >- https://api.modellix.ai/api/v1/tasks/task-gemini-38-tts-001 '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '429': $ref: '#/components/responses/TooManyRequests' '500': $ref: '#/components/responses/InternalServerError' components: schemas: Gemini38FlashTTSRequest: type: object description: >- Gemini 3.8 Flash TTS request. Single-speaker calls send text and voice, with optional style and language_code, and omit speakers and turns. Two-speaker calls send speakers (exactly 2) and turns, and must omit top-level text, voice, and style. style is delivery direction and is not spoken. text is the verbatim transcript. The combined text and trimmed style across the request must not exceed 8,192 Unicode characters. The 3.1 prompt field is not supported. For single-speaker synthesis, voice accepts a prebuilt name (such as Kore or Puck), an extended voice-library ID, or a voice_ / voicekey_ ID. Voice creation and management are not part of this endpoint. properties: text: type: string description: >- Verbatim transcript for single-speaker synthesis. Required in single-speaker mode. Do not include stage directions here. Inline vocal events use angle brackets. Together with style, the request must stay within 8,192 characters. minLength: 1 maxLength: 8192 example: Have a wonderful day! style: type: string description: >- Optional single-speaker delivery direction (emotion, pace, tone). Not spoken aloud. Max 8,192 characters, counted together with text. maxLength: 8192 example: cheerful and friendly language_code: type: string description: >- Optional BCP-47 language tag in lowercase. Examples: en-us, cmn-cn, ja-jp. The model can also detect the language from the transcript. pattern: ^[a-z]{2,3}(-[a-z0-9]+)*$ example: en-us voice: type: string description: >- Required for single-speaker synthesis. Prebuilt voice name, extended voice-library ID, or a designed/replicated voice ID (voice_... or voicekey_...). No spaces. Max 256 characters. minLength: 1 maxLength: 256 example: Kore speakers: type: array description: >- Required for two-speaker synthesis. Exactly two speakers. Omit this field for single-speaker calls. minItems: 2 maxItems: 2 items: $ref: '#/components/schemas/Gemini38TTSSpeaker' turns: type: array description: >- Required for two-speaker synthesis. One object per spoken turn, in order. Each speaker must match a name in speakers, case-sensitively. All turns produce one WAV file. The sum of all turn text and trimmed style must stay within 8,192 Unicode characters. minItems: 1 items: $ref: '#/components/schemas/Gemini38TTSTurn' AsyncTaskResponse: type: object required: - code - message - data properties: code: type: integer description: Response code, 0 indicates success example: 0 message: type: string description: Response message example: success data: type: object required: - status - task_id - model_id description: >- Task submission details. Poll GET /api/v1/tasks/{task_id} until status is success; audio appears in result.resources with type audio and format wav. properties: status: type: string enum: - pending - processing description: Initial task status example: pending task_id: type: string description: Unique task identifier for polling example: task-gemini-tts-001 model_id: type: string description: Model ID in provider/model format example: google/gemini-3.1-flash-tts get_result: type: object description: Endpoint to query the task result properties: method: type: string example: GET url: type: string example: https://api.modellix.ai/api/v1/tasks/task-gemini-tts-001 Gemini38TTSSpeaker: type: object required: - speaker - voice properties: speaker: type: string description: Speaker name used by turns. Alphanumeric, 1-64 characters. minLength: 1 maxLength: 64 pattern: ^[A-Za-z0-9]+$ example: Joe voice: type: string description: >- Preset Gemini voice name for this speaker, such as Puck or Kore. Designed or replicated voices (voice_... or voicekey_...) are not supported in dialogue. minLength: 1 maxLength: 256 example: Puck Gemini38TTSTurn: type: object required: - speaker - text properties: speaker: type: string description: Which configured speaker says this turn. minLength: 1 maxLength: 64 pattern: ^[A-Za-z0-9]+$ example: Joe text: type: string description: Verbatim line for this turn. minLength: 1 maxLength: 8192 example: How is it going today, Jane? style: type: string description: Optional delivery direction for this turn only. Not spoken aloud. maxLength: 8192 example: cheerful and friendly ErrorResponse: type: object required: - code - message properties: code: type: integer description: Error code (equals HTTP status code) example: 400 message: type: string description: 'Error message in format ''Category: detail''' example: 'Invalid parameters: combined prompt and text must be <= 8000 bytes' responses: BadRequest: description: Invalid request parameters content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: code: 400 message: 'Invalid parameters: parameter ''text'' is required' Unauthorized: description: Unauthorized - Invalid or missing API Key content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: code: 401 message: 'Authentication failed: invalid API key' TooManyRequests: description: Too many requests - Rate limit exceeded headers: X-RateLimit-Limit: description: Maximum requests per minute schema: type: integer example: 100 X-RateLimit-Remaining: description: Remaining quota in current window schema: type: integer example: 0 X-RateLimit-Reset: description: Rate limit window reset time (Unix timestamp) schema: type: integer example: 1704067260 content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: code: 429 message: >- Rate limit exceeded: 100 requests per minute, retry after 60 seconds InternalServerError: description: Internal server error content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: code: 500 message: Internal server error securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: API Key description: 'Modellix API Key. Format: `Bearer `' ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.