> ## Documentation Index > Fetch the complete documentation index at: https://heygen-1fa696a7.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Generate Speech > Generates speech using the voice identified by `voice_id` and returns a URL for one completed mono PCM16 WAV file at 44.1 kHz. The request remains open until synthesis and output assembly finish. The voice must be an ACTIVE professional voice. Rate limit: 30 requests per minute per workspace member. ## OpenAPI ````yaml /openapi/external-api.json post /v3/models/audio/tts openapi: 3.1.0 info: title: HeyGen External API version: 1.0.0 description: >- HeyGen's external API for programmatic AI video creation. See https://docs.heygen.com for full documentation. contact: name: HeyGen Product Infra url: https://heygen.com servers: - url: https://api.heygen.com description: Production security: - ApiKeyAuth: [] - BearerAuth: [] tags: - name: Video Agent description: Create videos from text prompts using AI - name: Videos description: Create, list, retrieve, and delete videos - name: Templates description: Generate videos from reusable templates by replacing their variables - name: Voices description: Text-to-speech and voice management - name: Audio description: Search the background-music and sound-effects catalog - name: Video Translate description: Translate videos into other languages - name: AI Clipping description: Turn long-form videos into ready-to-share short clips with captions - name: Batches description: Create and track batches of videos. - name: Video Translation Batches description: Create and track batches of video translations. - name: Lipsync Batches description: Create and track batches of lipsyncs. - name: Asset Batches description: Create and track batches of direct-to-S3 asset uploads. - name: User description: Account information and billing - name: API Keys description: Inspect the API key authenticating the current request - name: Avatars description: List and manage avatars and looks - name: Assets description: Upload files for use in video creation - name: Webhooks description: Manage webhook endpoints and events - name: Lipsync description: Dub or replace audio on existing videos - name: Brand description: >- Brand-related resources — brand kits (colors, fonts, logos) and brand glossaries (custom term translations) - name: HyperFrames description: Render HyperFrames composition zips into video — separate from /v3/videos - name: Models description: '' - name: Filler Word Removal description: '' paths: /v3/models/audio/tts: post: tags: - Models summary: Generate Speech description: >- Generates speech using the voice identified by `voice_id` and returns a URL for one completed mono PCM16 WAV file at 44.1 kHz. The request remains open until synthesis and output assembly finish. The voice must be an ACTIVE professional voice. Rate limit: 30 requests per minute per workspace member. operationId: generateModelSpeech requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/CreateSpeechRequest' responses: '200': description: Successful response content: application/json: schema: type: object properties: data: $ref: '#/components/schemas/CreateSpeechResponseData' '400': description: Invalid request parameters content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' examples: invalid_parameter: summary: Unsupported language value: error: code: invalid_parameter message: language is not a supported language. param: language doc_url: null voice_expired: summary: Professional voice clone over the workspace slot limit value: error: code: voice_expired message: >- Professional voice clone 'voice-1' expired because this workspace exceeded its professional voice clone slot limit of 2. Purchase more professional voice clone slots, or delete other professional voice clones to bring the workspace within its limit, then try again. param: null doc_url: null '401': description: Authentication failed content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: unauthorized message: API key or OAuth token required param: null doc_url: null '402': description: >- Payment required — `error.code` is one of: `insufficient_credit`, `plan_upgrade_required`. content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' examples: insufficient_credit: summary: Insufficient credits in the selected billing wallet value: error: code: insufficient_credit message: >- Insufficient credits. Please upgrade your plan or purchase additional credits. param: null doc_url: null plan_upgrade_required: summary: OAuth speech requires a paid plan value: error: code: plan_upgrade_required message: >- Professional voice speech through OAuth requires a paid plan. Please upgrade your subscription. param: null doc_url: null '403': description: Forbidden content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: forbidden message: >- The professional voice cloning API is not enabled for this account. param: null doc_url: null '404': description: Resource not found content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: voice_not_found message: Voice not found. param: null doc_url: null '409': description: >- Conflict — `error.code` is one of: `voice_not_ready`, `voice_training_failed`. content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' examples: voice_not_ready: summary: Voice training is not complete value: error: code: voice_not_ready message: The professional voice clone is not ready for inference. param: null doc_url: null voice_training_failed: summary: Voice training failed value: error: code: voice_training_failed message: The professional voice clone failed training. param: null doc_url: null '429': description: Rate limit exceeded content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: rate_limit_exceeded message: >- Too many requests. Retry after the duration specified in the Retry-After header. param: null doc_url: null headers: Retry-After: description: Seconds to wait before retrying schema: type: integer '502': description: >- Upstream dependency failed — the request did not complete and is safe to retry. content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: voice_provider_error message: The upstream voice provider failed. Retry the request. param: null doc_url: null '503': description: >- Temporarily unavailable — the request did not complete and is safe to retry. content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: service_unavailable message: Voice inference is temporarily busy. Retry the request. param: null doc_url: null '504': description: >- Upstream dependency timed out — the request did not complete and is safe to retry. content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: gateway_timeout message: The upstream voice provider timed out. Retry the request. param: null doc_url: null security: - ApiKeyAuth: [] - BearerAuth: [] components: schemas: CreateSpeechRequest: additionalProperties: false properties: voice_id: description: Identifier of the voice used for speech synthesis. minLength: 1 title: Voice Id type: string text: description: Plain text to synthesize. SSML and break tags are not supported. maxLength: 5000 minLength: 1 title: Text type: string language: description: Language code used for speech synthesis, such as `en`. minLength: 1 title: Language type: string seed: anyOf: - maximum: 4294967295 minimum: 0 type: integer - type: 'null' default: null description: Optional best-effort deterministic generation seed. title: Seed required: - voice_id - text - language title: CreateSpeechRequest type: object CreateSpeechResponseData: properties: audio_url: description: URL of the generated audio file. title: Audio Url type: string duration: description: Duration of the generated audio in seconds. minimum: 0 title: Duration type: number required: - audio_url - duration title: CreateSpeechResponseData type: object StandardAPIError: type: object properties: code: type: string description: Machine-readable error code example: invalid_parameter message: type: string description: Human-readable error message example: Video not found param: type: - string - 'null' description: Which request field caused the error doc_url: type: - string - 'null' description: Link to error documentation errors: type: array description: >- Per-item error details for batch/multi-node failures (e.g. graph compilation errors by node). items: $ref: '#/components/schemas/StandardAPIErrorDetail' required: - code - message StandardAPIErrorDetail: type: object properties: code: type: string description: Machine-readable error code example: unknown_node_type message: type: string description: Human-readable error message example: Unknown node type node_id: type: string description: Graph node id this error pertains to, if applicable port: type: string description: Port name on the node this error pertains to, if applicable path: type: string description: Field path within the item this error pertains to, if applicable required: - code - message securitySchemes: ApiKeyAuth: type: apiKey in: header name: x-api-key description: HeyGen API key. Obtain from your HeyGen dashboard. BearerAuth: type: http scheme: bearer description: OAuth2 bearer token. ````