> ## 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 3.1 Flash TTS > [Core Function] Gemini 3.1 Flash TTS is Google's low-latency, controllable text-to-speech model. [Strengths] Single-speaker and two-speaker dialogue, 30 prebuilt voices, 70+ languages via language_code, and expressive delivery through style prompts plus inline audio tags such as [whispers], [slow], [fast], and [laughs]. Output is WAV (24 kHz mono PCM). [Best For] Voiceovers, virtual presenters, audiobook narration, multilingual speech, podcast-style scripts, and two-person dialogue. [Limitations] Do NOT use for 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. Combined prompt and text must stay within 8,000 bytes. [Routing] Route here for controllable Gemini TTS from text only; for video with native audio use Veo; for talking-head lip sync from a portrait plus audio use Kling Avatar or SkyReels avatar models. ## OpenAPI ````yaml /model-api/google/google-t2s.json post /google/gemini-3.1-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-3.1-flash-tts: post: summary: Gemini 3.1 Flash TTS description: >- [Core Function] Gemini 3.1 Flash TTS is Google's low-latency, controllable text-to-speech model. [Strengths] Single-speaker and two-speaker dialogue, 30 prebuilt voices, 70+ languages via language_code, and expressive delivery through style prompts plus inline audio tags such as [whispers], [slow], [fast], and [laughs]. Output is WAV (24 kHz mono PCM). [Best For] Voiceovers, virtual presenters, audiobook narration, multilingual speech, podcast-style scripts, and two-person dialogue. [Limitations] Do NOT use for 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. Combined prompt and text must stay within 8,000 bytes. [Routing] Route here for controllable Gemini TTS from text only; for video with native audio use Veo; for talking-head lip sync from a portrait plus audio use Kling Avatar or SkyReels avatar models. operationId: gemini31FlashTTSAsync requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/Gemini31FlashTTSRequest' examples: single_speaker: summary: Single speaker with style prompt value: text: Hello, welcome to Modellix! prompt: Friendly and warm tone, cheerful and upbeat delivery language_code: en-us speakers: - speaker: Narrator voice: Kore dual_speaker: summary: Two-speaker dialogue value: text: |- Joe: Hi there! Jane: Hello, nice to meet you. language_code: en-us speakers: - speaker: Joe voice: Kore - speaker: Jane voice: Puck with_audio_tags: summary: Expressive delivery with audio tags value: text: >- [whispering] This is a secret. [short pause] But not for long! prompt: >- Dramatic suspenseful narration. Whisper the secret lines softly, then return to a tense, urgent tone. language_code: en-us speakers: - speaker: Narrator voice: Kore 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-tts-001 model_id: google/gemini-3.1-flash-tts get_result: method: GET url: https://api.modellix.ai/api/v1/tasks/task-gemini-tts-001 '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '429': $ref: '#/components/responses/TooManyRequests' '500': $ref: '#/components/responses/InternalServerError' components: schemas: Gemini31FlashTTSRequest: type: object required: - text - speakers description: >- Gemini 3.1 Flash TTS request. Always pass voice through speakers (1-2 items), even for single-speaker synthesis. When prompt is set, style and script are combined as "{prompt}: {text}". Byte limits apply to UTF-8 length (multibyte characters count toward the limit). properties: text: type: string description: >- Script to be spoken. Required. Max 8,000 bytes when used alone; if prompt is set, combined "{prompt}: {text}" must not exceed 8,000 bytes. When prompt is set, put only the spoken script here (do not repeat style instructions such as "Say cheerfully:" in text). May include inline audio tags such as [whispers], [slow], [fast], [laughs], and [short pause] to steer delivery. minLength: 1 maxLength: 8000 example: Hello, welcome to Modellix! prompt: type: string description: >- Optional director or style instruction (tone, pace, emotion, scene). Max 4,000 bytes. Merged with text as "{prompt}: {text}". Combined prompt + ": " + text must not exceed 8,000 bytes. If you omit prompt, you may embed direction in text using Google's single-field pattern (e.g. "Say cheerfully: ...") or audio tags. maxLength: 4000 example: Friendly and warm tone language_code: type: string description: >- Optional BCP-47 language and accent code. Examples: en-us, en-in, cmn-cn, ja-jp, ko-kr, fr-fr. pattern: ^[a-z]{2,3}(-[a-z0-9]+)*$ example: en-us speakers: type: array description: >- Speaker configuration. Required. Length 1 (single voice) or 2 (dialogue). Voice is always set here; there is no top-level voice field. minItems: 1 maxItems: 2 items: $ref: '#/components/schemas/TTSSpeaker' AsyncTaskResponse: type: object required: - code - message - data properties: code: type: integer description: Response code, 0 indicates success example: 0 message: type: string description: Response message example: success data: type: object required: - status - task_id - model_id description: >- Task submission details. Poll GET /api/v1/tasks/{task_id} until status is success; audio appears in result.resources with type audio and format wav. properties: status: type: string enum: - pending - processing description: Initial task status example: pending task_id: type: string description: Unique task identifier for polling example: task-gemini-tts-001 model_id: type: string description: Model ID in provider/model format example: google/gemini-3.1-flash-tts get_result: type: object description: Endpoint to query the task result properties: method: type: string example: GET url: type: string example: https://api.modellix.ai/api/v1/tasks/task-gemini-tts-001 TTSSpeaker: type: object required: - speaker - voice properties: speaker: type: string description: >- Speaker label. For dialogue, must match names used in text (e.g. "Joe: ..."). Alphanumeric only, 1-64 characters. minLength: 1 maxLength: 64 pattern: ^[A-Za-z0-9]+$ example: Narrator voice: type: string description: Prebuilt Gemini TTS voice name. enum: - Zephyr - Puck - Charon - Kore - Fenrir - Leda - Orus - Aoede - Callirrhoe - Autonoe - Enceladus - Iapetus - Umbriel - Algieba - Despina - Erinome - Algenib - Rasalgethi - Laomedeia - Achernar - Alnilam - Schedar - Gacrux - Pulcherrima - Achird - Zubenelgenubi - Sadachbia - Sadaltager - Sulafat - Vindemiatrix example: Kore 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 `' ````