> ## Documentation Index > Fetch the complete documentation index at: https://docs.slng.ai/llms.txt > Use this file to discover all available pages before exploring further. # Cartesia Sonic 3 > Stream low-latency speech synthesis from Cartesia Sonic 3 over WebSocket with a multilingual catalog of voices and context-aware controls. ## AsyncAPI ````yaml api-reference/asyncapi/tts-cartesia.asyncapi.yaml /v1/tts/cartesia/sonic:3 id: /v1/tts/cartesia/sonic:3 title: Cartesia Sonic 3 description: >- Stream low-latency speech synthesis from Cartesia Sonic 3 over WebSocket with a multilingual catalog of voices and context-aware controls. servers: - id: production protocol: wss host: api.slng.ai bindings: [] variables: [] - id: staging protocol: wss host: stageapi.slng.ai bindings: [] variables: [] address: /v1/tts/cartesia/sonic:3 parameters: [] bindings: - protocol: ws version: latest value: method: GET headers: type: object properties: X-World-Part-Override: type: string description: >- Target world part override. Auto-selected if not provided. Available world parts: `ap`, `eu`, `na`. enum: - ap - eu - na x-parser-schema-id: x-parser-schema-id: WebsocketHeadersCartesia schemaProperties: - name: method type: string description: GET required: false - name: headers type: object required: false properties: - name: X-World-Part-Override type: string description: >- Target world part override. Auto-selected if not provided. Available world parts: `ap`, `eu`, `na`. enumValues: - ap - eu - na required: false operations: - &ref_2 id: ttsCartesiaSonic3ReceiveInit title: Tts cartesia sonic3 receive init description: Initialize session on Cartesia Sonic 3 type: receive messages: - &ref_11 id: CartesiaSonicTtsInitRequest contentType: application/json payload: - name: Init Request (Cartesia Sonic 3) description: >- Initialize a Cartesia Sonic 3 TTS session with provider-specific configuration. type: object properties: - name: type type: string description: init required: true - name: model_id type: string description: Cartesia Sonic model identifier. enumValues: - sonic-3 required: false - name: voice type: string description: Cartesia voice identifier. required: false - name: language type: string description: Optional language override for supported Sonic 3 voices. required: false - name: encoding type: string description: Output audio encoding format. enumValues: - linear16 - mulaw - ulaw - alaw required: false - name: sample_rate type: integer description: Output audio sample rate in Hz. enumValues: - 8000 - 16000 - 24000 - 44100 required: false - name: context_id type: string description: >- Optional synthesis context identifier. If omitted, the gateway generates one per WebSocket session. required: false headers: [] jsonPayloadSchema: type: object description: >- Initialize a Cartesia Sonic 3 TTS session with voice, language, and audio format options. Fields set here are applied for the session unless overridden per text message. required: - type properties: type: type: string const: init default: init x-parser-schema-id: model_id: type: string description: Cartesia Sonic model identifier. enum: - sonic-3 default: sonic-3 x-parser-schema-id: voice: type: string description: Cartesia voice identifier. default: f786b574-daa5-4673-aa0c-cbe3e8534c02 x-parser-schema-id: language: type: string description: Optional language override for supported Sonic 3 voices. x-parser-schema-id: encoding: type: string description: Output audio encoding format. enum: - linear16 - mulaw - ulaw - alaw default: linear16 x-parser-schema-id: sample_rate: type: integer description: Output audio sample rate in Hz. enum: - 8000 - 16000 - 24000 - 44100 default: 24000 x-parser-schema-id: context_id: type: string description: >- Optional synthesis context identifier. If omitted, the gateway generates one per WebSocket session. x-parser-schema-id: x-parser-schema-id: title: Init Request (Cartesia Sonic 3) description: >- Initialize a Cartesia Sonic 3 TTS session with provider-specific configuration. example: |- { "type": "init", "model_id": "sonic-3", "voice": "f786b574-daa5-4673-aa0c-cbe3e8534c02", "encoding": "linear16", "sample_rate": 24000 } bindings: [] extensions: - id: x-parser-unique-object-id value: CartesiaSonicTtsInitRequest bindings: [] extensions: &ref_0 - id: x-parser-unique-object-id value: /v1/tts/cartesia/sonic:3 - &ref_3 id: ttsCartesiaSonic3ReceiveText title: Tts cartesia sonic3 receive text description: Send text to Cartesia Sonic 3 type: receive messages: - &ref_12 id: CartesiaSonicTtsTextMessage contentType: application/json payload: - name: Text Message (Cartesia Sonic 3) description: >- Send text to synthesize on Cartesia Sonic 3 with optional generation controls. type: object properties: - name: type type: string description: text required: true - name: text type: string description: Text to synthesize. required: true - name: voice type: string description: Override the Cartesia voice identifier for this utterance. required: false - name: generation_config type: object description: >- Optional Sonic 3 generation controls such as speed, volume, and emotion. required: false properties: - name: speed type: number description: Sonic 3 speed multiplier guidance. required: false - name: volume type: number description: Sonic 3 volume multiplier guidance. required: false - name: emotion type: string description: Sonic 3 emotional guidance. required: false - name: speed type: string description: >- Deprecated Cartesia speed override. Prefer `generation_config.speed` for Sonic 3. Ignored when `generation_config` is provided. enumValues: - slow - normal - fast required: false - name: continue type: boolean description: >- Whether more text inputs may follow on the same `context_id`. When `true`, Cartesia keeps the context open and waits. When `false` or omitted, this is the final input — Cartesia emits the trailing audio and then `audio_end`. required: false - name: max_buffer_delay_ms type: integer description: >- Maximum time, in milliseconds, that Cartesia buffers incoming text before starting generation. Use it to group several quick `text` inputs into a single synthesis pass — the longer the delay, the more text Cartesia can combine. Omit or set `0` to generate as soon as the first text input arrives. required: false - name: add_timestamps type: boolean description: >- Whether Cartesia should emit timestamp events for this generation. required: false - name: flush type: boolean description: >- Marks a segment boundary within the active context. Not required to receive audio — Cartesia begins generating as soon as text arrives. Sending `flush: true` increments the `flush_id` that Cartesia includes on subsequent `audio_chunk` frames so you can correlate audio back to the text segment that produced it. Does not finalize the context; complete generation by sending the final input with `continue: false`. required: false - name: pronunciation_dict_id type: string description: >- Optional pronunciation dictionary applied to this generation only. required: false - name: context_id type: string description: >- Optional synthesis context identifier. If omitted, the gateway uses the active session context_id. required: false headers: [] jsonPayloadSchema: type: object description: >- Send text to synthesize into audio output using Cartesia Sonic 3. Supports per-utterance generation controls including speed, volume, emotion, and manual flushing. required: - type - text properties: type: type: string const: text x-parser-schema-id: text: type: string minLength: 1 description: Text to synthesize. x-parser-schema-id: voice: type: string description: Override the Cartesia voice identifier for this utterance. x-parser-schema-id: generation_config: type: object description: >- Optional Sonic 3 generation controls such as speed, volume, and emotion. properties: speed: type: number minimum: 0.6 maximum: 1.5 description: Sonic 3 speed multiplier guidance. x-parser-schema-id: volume: type: number minimum: 0.5 maximum: 2 description: Sonic 3 volume multiplier guidance. x-parser-schema-id: emotion: type: string description: Sonic 3 emotional guidance. x-parser-schema-id: x-parser-schema-id: speed: type: string description: >- Deprecated Cartesia speed override. Prefer `generation_config.speed` for Sonic 3. Ignored when `generation_config` is provided. enum: - slow - normal - fast x-parser-schema-id: continue: type: boolean description: >- Whether more text inputs may follow on the same `context_id`. When `true`, Cartesia keeps the context open and waits. When `false` or omitted, this is the final input — Cartesia emits the trailing audio and then `audio_end`. x-parser-schema-id: max_buffer_delay_ms: type: integer minimum: 0 maximum: 5000 description: >- Maximum time, in milliseconds, that Cartesia buffers incoming text before starting generation. Use it to group several quick `text` inputs into a single synthesis pass — the longer the delay, the more text Cartesia can combine. Omit or set `0` to generate as soon as the first text input arrives. x-parser-schema-id: add_timestamps: type: boolean description: >- Whether Cartesia should emit timestamp events for this generation. x-parser-schema-id: flush: type: boolean description: >- Marks a segment boundary within the active context. Not required to receive audio — Cartesia begins generating as soon as text arrives. Sending `flush: true` increments the `flush_id` that Cartesia includes on subsequent `audio_chunk` frames so you can correlate audio back to the text segment that produced it. Does not finalize the context; complete generation by sending the final input with `continue: false`. x-parser-schema-id: pronunciation_dict_id: type: string description: >- Optional pronunciation dictionary applied to this generation only. x-parser-schema-id: context_id: type: string description: >- Optional synthesis context identifier. If omitted, the gateway uses the active session context_id. x-parser-schema-id: x-parser-schema-id: title: Text Message (Cartesia Sonic 3) description: >- Send text to synthesize on Cartesia Sonic 3 with optional generation controls. example: |- { "type": "text", "text": "Hello, this is Cartesia Sonic 3." } bindings: [] extensions: - id: x-parser-unique-object-id value: CartesiaSonicTtsTextMessage bindings: [] extensions: *ref_0 - &ref_4 id: ttsCartesiaSonic3ReceiveFlush title: Tts cartesia sonic3 receive flush description: Flush buffered output on Cartesia Sonic 3 type: receive messages: - &ref_13 id: TtsFlushMessage contentType: application/json payload: - name: Flush Message description: >- Standalone segment boundary on the active Cartesia Sonic 3 context. type: object properties: - name: type type: string description: flush required: true headers: [] jsonPayloadSchema: type: object description: >- Standalone segment boundary on the active context. Has the same effect as setting `flush: true` on a `text` input: it increments `flush_id` and does not finalize the context. Complete generation by sending the final `text` input with `continue: false`. required: - type properties: type: type: string const: flush x-parser-schema-id: x-parser-schema-id: title: Flush Message description: Standalone segment boundary on the active Cartesia Sonic 3 context. example: |- { "type": "flush" } bindings: [] extensions: - id: x-parser-unique-object-id value: TtsFlushMessage bindings: [] extensions: *ref_0 - &ref_5 id: ttsCartesiaSonic3ReceiveCancel title: Tts cartesia sonic3 receive cancel description: Cancel in-progress generation on Cartesia Sonic 3 type: receive messages: - &ref_14 id: TtsCancelMessage contentType: application/json payload: - name: Cancel Message description: Cancel an in-progress Cartesia Sonic 3 synthesis context. type: object properties: - name: type type: string description: cancel required: true - name: context_id type: string description: >- Optional context identifier to cancel. If omitted, the gateway cancels the active session context_id. required: false headers: [] jsonPayloadSchema: type: object description: >- Cancel an in-progress Cartesia synthesis context. The gateway forwards a native `{ context_id, cancel: true }` frame to Cartesia. When `context_id` is omitted, the active session context is cancelled. Cartesia recommends starting a new `context_id` for the next turn after a cancel. required: - type properties: type: type: string const: cancel x-parser-schema-id: context_id: type: string description: >- Optional context identifier to cancel. If omitted, the gateway cancels the active session context_id. x-parser-schema-id: x-parser-schema-id: title: Cancel Message description: Cancel an in-progress Cartesia Sonic 3 synthesis context. example: |- { "type": "cancel" } bindings: [] extensions: - id: x-parser-unique-object-id value: TtsCancelMessage bindings: [] extensions: *ref_0 - &ref_6 id: ttsCartesiaSonic3ReceiveClose title: Tts cartesia sonic3 receive close description: Close session on Cartesia Sonic 3 type: receive messages: - &ref_15 id: TtsCloseMessage contentType: application/json payload: - name: Close Message description: Close the session and stop any further audio. type: object properties: - name: type type: string description: close required: true headers: [] jsonPayloadSchema: type: object description: Close the session and stop any further audio. required: - type properties: type: type: string const: close x-parser-schema-id: x-parser-schema-id: title: Close Message description: Close the session and stop any further audio. example: |- { "type": "close" } bindings: [] extensions: - id: x-parser-unique-object-id value: TtsCloseMessage bindings: [] extensions: *ref_0 - &ref_7 id: ttsCartesiaSonic3ReceiveKeepalive title: Tts cartesia sonic3 receive keepalive description: Send keepalive on Cartesia Sonic 3 type: receive messages: - &ref_16 id: KeepaliveMessage contentType: application/json payload: - name: Keepalive Message description: Keep the WebSocket connection alive during silence. type: object properties: - name: type type: string description: keepalive required: true headers: [] jsonPayloadSchema: type: object description: >- Prevents the connection from being closed due to inactivity. Send periodically during silence to maintain the session. required: - type properties: type: type: string const: keepalive x-parser-schema-id: x-parser-schema-id: title: Keepalive Message description: Keep the WebSocket connection alive during silence. example: |- { "type": "keepalive" } bindings: [] extensions: - id: x-parser-unique-object-id value: KeepaliveMessage bindings: [] extensions: *ref_0 - &ref_8 id: ttsCartesiaSonic3SendAudioChunk title: Tts cartesia sonic3 send audio chunk description: Receive audio chunk from Cartesia Sonic 3 type: send messages: - &ref_17 id: CartesiaSonicTtsAudioChunk contentType: application/json payload: - name: Audio Chunk (Cartesia Sonic 3) description: Streaming audio chunk from Cartesia Sonic 3. type: object properties: - name: type type: string description: audio_chunk required: true - name: data type: string description: >- Base64-encoded audio chunk matching the requested encoding and sample rate. required: true - name: done type: boolean description: True when this is the final chunk of the active context. required: false - name: status_code type: integer description: Upstream HTTP-equivalent status code from Cartesia. required: false - name: step_time type: number description: Cartesia processing time for this chunk, in milliseconds. required: false - name: flush_id type: integer description: >- Segment identifier within the active context. Starts at `0` and increments by `1` each time a `text` input is sent with `flush: true`, or whenever a standalone flush message is issued. Use it to correlate audio chunks back to the text segment that produced them. required: false - name: context_id type: string description: Synthesis context identifier this chunk belongs to. required: false headers: [] jsonPayloadSchema: type: object description: >- Streaming audio chunk emitted by Cartesia Sonic 3. The gateway forwards each upstream `chunk` message as an `audio_chunk`, preserving Cartesia's native fields. required: - type - data properties: type: type: string const: audio_chunk x-parser-schema-id: data: type: string format: byte description: >- Base64-encoded audio chunk matching the requested encoding and sample rate. x-parser-schema-id: done: type: boolean description: True when this is the final chunk of the active context. x-parser-schema-id: status_code: type: integer description: Upstream HTTP-equivalent status code from Cartesia. x-parser-schema-id: step_time: type: number description: Cartesia processing time for this chunk, in milliseconds. x-parser-schema-id: flush_id: type: integer description: >- Segment identifier within the active context. Starts at `0` and increments by `1` each time a `text` input is sent with `flush: true`, or whenever a standalone flush message is issued. Use it to correlate audio chunks back to the text segment that produced them. x-parser-schema-id: context_id: type: string description: Synthesis context identifier this chunk belongs to. x-parser-schema-id: x-parser-schema-id: title: Audio Chunk (Cartesia Sonic 3) description: Streaming audio chunk from Cartesia Sonic 3. example: |- { "type": "audio_chunk", "context_id": "9baf38d7-799e-40f2-88d1-daeacbdb3910", "status_code": 206, "done": false, "data": "AAF+/dD7n/wj/rD/owGoBEQHBgjTBcoDjAITAk0BtwF0BFUI5wmlB7cEAgO3ArIBUwB0AJwDDQbQBacCEgDA/vD96vxr/H3+hwAqASr/Z/3C/BEAEQAUAA==", "step_time": 67.49622, "flush_id": 0 } bindings: [] extensions: - id: x-parser-unique-object-id value: CartesiaSonicTtsAudioChunk bindings: [] extensions: *ref_0 - &ref_9 id: ttsCartesiaSonic3SendAudioEnd title: Tts cartesia sonic3 send audio end description: Receive audio end from Cartesia Sonic 3 type: send messages: - &ref_18 id: TtsAudioEnd contentType: application/json payload: - name: Audio End description: Signals the end of audio generation. type: object properties: - name: type type: string description: audio_end required: true - name: done type: boolean description: Always `true` on Cartesia generation-complete frames. required: false - name: status_code type: integer description: Upstream HTTP-equivalent status code from Cartesia. required: false - name: context_id type: string description: Synthesis context identifier that finished generation. required: false headers: [] jsonPayloadSchema: type: object description: >- Signals the end of audio generation for the active context. The gateway maps the upstream Cartesia `done` message to `audio_end`, preserving Cartesia's native fields. required: - type properties: type: type: string const: audio_end x-parser-schema-id: done: type: boolean description: Always `true` on Cartesia generation-complete frames. x-parser-schema-id: status_code: type: integer description: Upstream HTTP-equivalent status code from Cartesia. x-parser-schema-id: context_id: type: string description: Synthesis context identifier that finished generation. x-parser-schema-id: x-parser-schema-id: title: Audio End description: Signals the end of audio generation. example: |- { "type": "audio_end", "context_id": "9baf38d7-799e-40f2-88d1-daeacbdb3910", "status_code": 200, "done": true } bindings: [] extensions: - id: x-parser-unique-object-id value: TtsAudioEnd bindings: [] extensions: *ref_0 - &ref_10 id: ttsCartesiaSonic3SendError title: Tts cartesia sonic3 send error description: Receive error from Cartesia Sonic 3 type: send messages: - &ref_19 id: TtsErrorResponse contentType: application/json payload: - name: Error Response description: Indicates an error occurred during synthesis. type: object properties: - name: type type: string description: error required: true - name: message type: string description: Human-readable error description. required: true - name: title type: string description: Short error title from the upstream provider. required: false - name: status_code type: integer description: Upstream HTTP-equivalent status code. required: false - name: error_code type: &ref_1 - string - 'null' description: Provider-specific error code, when available. required: false - name: done type: boolean description: >- True when the upstream marked the context as terminated by this error. required: false - name: request_id type: string description: Cartesia request identifier, useful when contacting support. required: false - name: doc_url type: string description: >- Cartesia documentation link for this error class, when provided. required: false - name: context_id type: string description: Synthesis context identifier associated with the error. required: false headers: [] jsonPayloadSchema: type: object description: >- Indicates an error occurred during synthesis. The gateway surfaces upstream Cartesia error messages with the original status code, provider-specific error code, and supporting metadata. required: - type - message properties: type: type: string const: error x-parser-schema-id: message: type: string description: Human-readable error description. x-parser-schema-id: title: type: string description: Short error title from the upstream provider. x-parser-schema-id: status_code: type: integer description: Upstream HTTP-equivalent status code. x-parser-schema-id: error_code: type: *ref_1 description: Provider-specific error code, when available. x-parser-schema-id: done: type: boolean description: >- True when the upstream marked the context as terminated by this error. x-parser-schema-id: request_id: type: string description: Cartesia request identifier, useful when contacting support. x-parser-schema-id: doc_url: type: string description: Cartesia documentation link for this error class, when provided. x-parser-schema-id: context_id: type: string description: Synthesis context identifier associated with the error. x-parser-schema-id: x-parser-schema-id: title: Error Response description: Indicates an error occurred during synthesis. example: |- { "type": "error", "message": "Provider returned an unexpected error", "status_code": 500, "error_code": "provider_error", "done": true, "request_id": "req-9b1c2f", "doc_url": "https://docs.cartesia.ai/errors/provider_error", "context_id": "demo-context-123" } bindings: [] extensions: - id: x-parser-unique-object-id value: TtsErrorResponse bindings: [] extensions: *ref_0 sendOperations: - *ref_2 - *ref_3 - *ref_4 - *ref_5 - *ref_6 - *ref_7 receiveOperations: - *ref_8 - *ref_9 - *ref_10 sendMessages: - *ref_11 - *ref_12 - *ref_13 - *ref_14 - *ref_15 - *ref_16 receiveMessages: - *ref_17 - *ref_18 - *ref_19 extensions: - id: x-parser-unique-object-id value: /v1/tts/cartesia/sonic:3 securitySchemes: - id: bearer name: bearer type: http description: > API key issued by SLNG. Pass as `Authorization: Bearer ` in the WebSocket upgrade request headers. scheme: bearer extensions: [] ````