> ## Documentation Index > Fetch the complete documentation index at: https://docs.zeroruntime.ai/llms.txt > Use this file to discover all available pages before exploring further. # Pipeline > JavaScript API reference for Pipeline. ## Pipeline Create a Pipeline from the given component PipelineOptions. ### Constructor ```typescript theme={null} new Pipeline(opts: PipelineOptions) ``` Speech-to-text provider. Defaults to `null`. Language-model provider. Defaults to `null`. Text-to-speech provider. Defaults to `null`. Voice-activity-detection provider. Defaults to `null`. End-of-turn detector. Defaults to `null`. Avatar/video provider. Defaults to `null`. Audio denoiser. Defaults to `null`. End-of-utterance config. Defaults to `EOUConfig()`. Interruption-handling config. Defaults to `InterruptConfig()`. Conversational-graph routing config. Defaults to `null`. Context-window trimming policy. Defaults to `null`. Voicemail detector. Defaults to `null`. DTMF (touch-tone) handler. Defaults to `null`. Realtime speech-to-speech config. Defaults to `null`. Enable the streaming LLM token-rewrite hook. Defaults to `false`. Per-token timeout for the LLM stream hook, in milliseconds. Defaults to `100`. Grace period in milliseconds before considering playback finished. Defaults to `0`. Regex patterns to drop from transcripts. Defaults to DEFAULT\_STT\_FILTER\_PATTERNS. Word replacements applied to transcripts (`{ from: to }`). Defaults to `{}`. Seconds of inactivity before the session times out, or `null` to disable. Defaults to `null`. Seconds of caller silence before the agent's `onWakeUp` hook fires, or `null` to disable. Defaults to `null`. Maximum wake-up nudges before the call ends, or `null` for no cap. Defaults to `null`. Drop a transcript that consists solely of a filler word ("okay", "yeah", ...) without an LLM turn. Defaults to `false` (every transcript reaches the model). Filler words used when PipelineOptions.filterFillerWords is on. When unset, the runtime supplies its own defaults. ### changeComponent ```typescript theme={null} changeComponent(opts: ChangeComponentOptions = {}): Promise ``` Hot-swap components that already exist in the pipeline, in place. Invalid swaps warn and are skipped; `passContext: false` clears the LLM's history (only after the runtime confirms the swap succeeded). ### changePipeline ```typescript theme={null} changePipeline(opts: ChangePipelineOptions = {}): Promise ``` Replace the whole pipeline mid-session (live mode switch): pass the complete target pipeline; the mode is inferred from the `llm`/components you pass. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getLatestFrames ```typescript theme={null} getLatestFrames(numFrames = 1): any[] ``` Return the most recent captured vision frames. Number of frames to return (most recent). Defaults to `1`. ### getSessionMetricsSnapshot ```typescript theme={null} getSessionMetricsSnapshot(): Record ``` Snapshot of session metrics (empty in this SDK build). ### interrupt ```typescript theme={null} interrupt(): void ``` Interrupt the bound agent's current turn. ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, callback?: PipelineHookFn): any ``` Register a hook for `event`. Usable directly (`on(event, fn)`) or as a decorator factory (`on(event)`). Delegates to Pipeline.hooks. ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### processText ```typescript theme={null} processText(text: string): Promise ``` Feed `text` into the bound agent's session as model input. ### pushAudioFrame ```typescript theme={null} pushAudioFrame(frame: any): void ``` Fire `audio_delta` hooks for an incoming audio frame. ### pushVisionFrame ```typescript theme={null} pushVisionFrame(frame: any): void ``` Buffer a vision frame (capped at VISION\_FRAME\_BUFFER\_MAX) and fire `vision_frame` hooks. ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` ### replyWithContext ```typescript theme={null} replyWithContext(instructions: string, extras: Record = {}): Promise ``` Generate a reply to `instructions` on the bound agent's session. ### sendMessage ```typescript theme={null} sendMessage(text: string, extras: Record = {}): Promise ``` Speak `text` on the bound agent's session. ### setAgent ```typescript theme={null} setAgent(agent: any): void ``` Bind the agent that runs on this pipeline. *** ## PipelineHooks Registry of pipeline hooks. Accessed via Pipeline.hooks or `Pipeline.on(...)`; lets you observe or transform audio, transcripts, LLM tokens, and lifecycle events. ### Constructor ```typescript theme={null} new PipelineHooks() ``` ### clearAllHooks ```typescript theme={null} clearAllHooks(): void ``` Remove all registered hooks. ### getHooks ```typescript theme={null} getHooks(event: string): PipelineHookFn[] ``` All multi-handler callbacks registered for `event`. ### hasLlmObservationHooks ```typescript theme={null} hasLlmObservationHooks(): boolean ``` Whether any observe-only `llm` hooks are registered. ### hasLlmStreamHook ```typescript theme={null} hasLlmStreamHook(): boolean ``` Whether an LLM stream hook is registered. ### hasSttStreamHook ```typescript theme={null} hasSttStreamHook(): boolean ``` Whether an STT stream hook is registered. ### hasTtsStreamHook ```typescript theme={null} hasTtsStreamHook(): boolean ``` Whether a TTS stream hook is registered. ### on ```typescript theme={null} on(event: string, fn?: PipelineHookFn): PipelineHookFn | ((fn: PipelineHookFn) => PipelineHookFn) ``` ### registeredNames ```typescript theme={null} registeredNames(): string[] ``` Names of all hooks that currently have at least one handler. *** ## PipelineHookError Thrown when a registered pipeline hook is not supported. ### Constructor ```typescript theme={null} new PipelineHookError(hookName: string, reason: string, alternative: string | null) ``` *** ## PipelineComponent A processing component that can be present in a Pipeline. ```typescript theme={null} enum PipelineComponent { STT = 'stt', LLM = 'llm', TTS = 'tts', VAD = 'vad', TURN_DETECTOR = 'turn_detector', AVATAR = 'avatar', DENOISE = 'denoise', REALTIME_MODEL = 'realtime_model', } ``` *** ## PipelineConfig Create a PipelineConfig. ### Constructor ```typescript theme={null} new PipelineConfig(opts: { /** Overall pipeline shape. */ pipelineMode: PipelineMode; /** Realtime wiring, or `null` for a non-realtime pipeline. */ realtimeMode: RealtimeMode | null; /** Whether a realtime model is in use. */ isRealtime: boolean; /** Components present in the pipeline. */ activeComponents: Iterable; }) ``` Overall pipeline shape. Realtime wiring, or `null` for a non-realtime pipeline. Whether a realtime model is in use. Components present in the pipeline. ### hasComponent ```typescript theme={null} hasComponent(component: PipelineComponent): boolean ``` Whether the given component is part of this pipeline. *** ## PipelineMode The shape of the configured pipeline, derived from which components (PipelineComponent) are present. Determined automatically from the Pipeline you build; not normally set by hand. ```typescript theme={null} enum PipelineMode { REALTIME = 'realtime', FULL_CASCADING = 'full_cascading', LLM_TTS_ONLY = 'llm_tts_only', STT_LLM_ONLY = 'stt_llm_only', LLM_ONLY = 'llm_only', STT_ONLY = 'stt_only', TTS_ONLY = 'tts_only', STT_TTS_ONLY = 'stt_tts_only', HYBRID = 'hybrid', PARTIAL_CASCADING = 'partial_cascading', } ``` *** ## RealtimeMode How a realtime speech-to-speech model is wired into the pipeline. ```typescript theme={null} enum RealtimeMode { FULL_S2S = 'full_s2s', HYBRID_STT = 'hybrid_stt', HYBRID_TTS = 'hybrid_tts', LLM_ONLY = 'llm_only', } ``` *** ## STT Base class for speech-to-text providers. Provider plugins (e.g. `DeepgramSTT({...})`) extend this; subclass it only to integrate a custom STT. ### Constructor ```typescript theme={null} new STT() ``` ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` Provider configuration sent to the Zero Runtime. Override to supply settings. ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### onSttTranscript ```typescript theme={null} onSttTranscript(callback: SttTranscriptCallback): void ``` Register a callback to receive transcripts as they are produced. ### processAudio ```typescript theme={null} processAudio(_audioFrames: Uint8Array, _language?: string | null, ..._extra: any[]): Promise ``` Process a buffer of audio frames. Override in a custom provider. ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` ### streamTranscribe ```typescript theme={null} streamTranscribe(_audioStream: AsyncIterable, ..._extra: any[]): AsyncIterator ``` Transcribe a streaming audio source, yielding STTResponses. Override in a custom provider. *** ## STTResponse Create an STTResponse. ### Constructor ```typescript theme={null} new STTResponse(init: { eventType: SpeechEventType; data: SpeechData; metadata?: Record | null; }) ``` *** ## SpeechData Create SpeechData. ### Constructor ```typescript theme={null} new SpeechData(init: { text: string; confidence?: number; language?: string | null; startTime?: number; endTime?: number; duration?: number; }) ``` *** ## LLM Base class for language-model providers. Provider plugins (e.g. `GoogleLLM({...})`) extend this; subclass it only to integrate a custom LLM. ### Constructor ```typescript theme={null} new LLM() ``` ### cancelCurrentGeneration ```typescript theme={null} cancelCurrentGeneration(): Promise ``` Cancel the in-flight generation for the current session, if any. ### chat ```typescript theme={null} chat(_messages: any, _opts?: LLMChatOptions): AsyncIterator ``` Stream a completion for the given messages, yielding LLMResponse chunks. ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` Provider configuration sent to the Zero Runtime. Override to supply settings. ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` *** ## LLMResponse Create an LLMResponse. ### Constructor ```typescript theme={null} new LLMResponse(init: { content: string; role: ChatRole; metadata?: Record | null; }) ``` *** ## TTS Base class for text-to-speech providers. Provider plugins (e.g. `CartesiaTTS({...})`) extend this; subclass it only to integrate a custom TTS. ### Constructor ```typescript theme={null} new TTS(opts: TTSOptions) ``` Output sample rate in Hz. Defaults to `24000`. Number of output channels. Defaults to `1`. ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` Provider configuration sent to the Zero Runtime. Override to supply settings. ### interrupt ```typescript theme={null} interrupt(): Promise ``` Stop the current synthesis. ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### onFirstAudioByte ```typescript theme={null} onFirstAudioByte(callback: FirstAudioByteCallback): void ``` Register a callback fired when the first synthesized audio byte is emitted. ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` ### synthesize ```typescript theme={null} synthesize(text: any, ..._extra: any[]): Promise ``` Synthesize and speak `text` on the active session. *** ## VAD Base class for voice-activity-detection providers. Provider plugins extend this; subclass it only to integrate a custom VAD. ### Constructor ```typescript theme={null} new VAD(opts: VADOptions) ``` Input sample rate in Hz. Defaults to `16000`. Speech-probability threshold 0-1 above which audio counts as speech. Defaults to `0.5`. Minimum speech duration in seconds to register a start-of-speech. Defaults to `0.5`. Minimum silence duration in seconds to register an end-of-speech. Defaults to `0.5`. ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### flush ```typescript theme={null} flush(): Promise ``` Flush any buffered audio. ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` Provider configuration (threshold and durations) sent to the Zero Runtime. ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### onVadEvent ```typescript theme={null} onVadEvent(callback: VadEventCallback): void ``` Register a callback to receive VADResponse events. ### processAudio ```typescript theme={null} processAudio(_audioFrames: Uint8Array, ..._extra: any[]): Promise ``` Process a buffer of audio frames. Override in a custom provider. ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` *** ## VADResponse Create a VADResponse. ### Constructor ```typescript theme={null} new VADResponse(init: { eventType: VADEventType; data: VADData; metadata?: Record | null; }) ``` *** ## VADData Create VADData. ### Constructor ```typescript theme={null} new VADData(init: { isSpeech: boolean; confidence?: number; timestamp?: number; speechDuration?: number; silenceDuration?: number; }) ``` *** ## EOU Base class for end-of-utterance (turn-detection) providers. Provider plugins extend this; subclass it only to integrate a custom turn detector. ### Constructor ```typescript theme={null} new EOU(opts: EOUOptions) ``` End-of-utterance probability threshold 0-1. Defaults to `0.7`. ### cleanup ```typescript theme={null} cleanup(): Promise ``` Tear down provider state. ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### detectEndOfUtterance ```typescript theme={null} detectEndOfUtterance(chatContext?: any, threshold?: number): boolean ``` Whether the current EOU probability meets `threshold` (or the configured one). ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getEouProbability ```typescript theme={null} getEouProbability(_chatContext?: any): number ``` Latest end-of-utterance probability 0-1 (defaults to `0.5` when unknown). ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` Provider configuration (threshold) sent to the Zero Runtime. ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` ### setThreshold ```typescript theme={null} setThreshold(threshold: number): void ``` Update the end-of-utterance threshold. *** ## FallbackSTT Create an STT provider that tries each provider in order, failing over to the next when one is unavailable. ### Constructor ```typescript theme={null} new FallbackSTT(providers: STT[], opts: FallbackOptions) ``` Providers in priority order; the first is the primary. Seconds to skip a failing provider before retrying. Defaults to DEFAULT\_TEMPORARY\_DISABLE\_SEC. Failed attempts after which a provider is disabled for the session. Defaults to DEFAULT\_PERMANENT\_DISABLE\_AFTER\_ATTEMPTS. Seconds between health checks of a disabled provider. Defaults to DEFAULT\_RECOVERY\_CHECK\_INTERVAL\_SEC. Latency ceiling in ms for the active provider. When exceeded for `consecutiveLatencyHits` turns in a row, the chain fails over. Omitted/0 = disabled. Consecutive turns over `latencyThresholdMs` before failing over. Defaults to 3. ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### onSttTranscript ```typescript theme={null} onSttTranscript(callback: SttTranscriptCallback): void ``` Register a callback to receive transcripts as they are produced. ### processAudio ```typescript theme={null} processAudio(_audioFrames: Uint8Array, _language?: string | null, ..._extra: any[]): Promise ``` Process a buffer of audio frames. Override in a custom provider. ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` ### streamTranscribe ```typescript theme={null} streamTranscribe(_audioStream: AsyncIterable, ..._extra: any[]): AsyncIterator ``` Transcribe a streaming audio source, yielding STTResponses. Override in a custom provider. *** ## FallbackLLM Create an LLM provider that tries each provider in order, failing over to the next when one is unavailable. The primary's `temperature` and `max_output_tokens` settings carry through. ### Constructor ```typescript theme={null} new FallbackLLM(providers: LLM[], opts: FallbackOptions) ``` Providers in priority order; the first is the primary. Seconds to skip a failing provider before retrying. Defaults to DEFAULT\_TEMPORARY\_DISABLE\_SEC. Failed attempts after which a provider is disabled for the session. Defaults to DEFAULT\_PERMANENT\_DISABLE\_AFTER\_ATTEMPTS. Seconds between health checks of a disabled provider. Defaults to DEFAULT\_RECOVERY\_CHECK\_INTERVAL\_SEC. Latency ceiling in ms for the active provider. When exceeded for `consecutiveLatencyHits` turns in a row, the chain fails over. Omitted/0 = disabled. Consecutive turns over `latencyThresholdMs` before failing over. Defaults to 3. ### cancelCurrentGeneration ```typescript theme={null} cancelCurrentGeneration(): Promise ``` Cancel the in-flight generation for the current session, if any. ### chat ```typescript theme={null} chat(_messages: any, _opts?: LLMChatOptions): AsyncIterator ``` Stream a completion for the given messages, yielding LLMResponse chunks. ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` *** ## FallbackTTS Create a TTS provider that tries each provider in order, failing over to the next when one is unavailable. ### Constructor ```typescript theme={null} new FallbackTTS(providers: TTS[], opts: FallbackOptions) ``` Providers in priority order; the first is the primary. Seconds to skip a failing provider before retrying. Defaults to DEFAULT\_TEMPORARY\_DISABLE\_SEC. Failed attempts after which a provider is disabled for the session. Defaults to DEFAULT\_PERMANENT\_DISABLE\_AFTER\_ATTEMPTS. Seconds between health checks of a disabled provider. Defaults to DEFAULT\_RECOVERY\_CHECK\_INTERVAL\_SEC. Latency ceiling in ms for the active provider. When exceeded for `consecutiveLatencyHits` turns in a row, the chain fails over. Omitted/0 = disabled. Consecutive turns over `latencyThresholdMs` before failing over. Defaults to 3. ### close ```typescript theme={null} close(): Promise ``` Release any resources held by the provider. ### closeEmitter ```typescript theme={null} closeEmitter(): Promise ``` Close the emitter: drop all handlers and stop emitting. Waits up to 2 seconds for in-flight async handlers to settle before returning. ### emit ```typescript theme={null} emit(event: string, ...args: any[]): void ``` ### getRuntimeConfig ```typescript theme={null} getRuntimeConfig(): Record ``` ### interrupt ```typescript theme={null} interrupt(): Promise ``` Stop the current synthesis. ### listenerCount ```typescript theme={null} listenerCount(event: string): number ``` ### off ```typescript theme={null} off(event: string, handler: EventHandler): void ``` ### on ```typescript theme={null} on(event: string, handler: EventHandler): EventHandler ``` ### once ```typescript theme={null} once(event: string, handler: EventHandler): EventHandler ``` ### onFirstAudioByte ```typescript theme={null} onFirstAudioByte(callback: FirstAudioByteCallback): void ``` Register a callback fired when the first synthesized audio byte is emitted. ### removeAllListeners ```typescript theme={null} removeAllListeners(event?: string): void ``` ### synthesize ```typescript theme={null} synthesize(text: any, ..._extra: any[]): Promise ``` Synthesize and speak `text` on the active session. *** ## UtteranceHandle See the class-level description for usage. ### Constructor ```typescript theme={null} new UtteranceHandle(opts: UtteranceHandleOptions) ``` Identifier for the utterance. Default: a generated UUID. Whether the utterance can be interrupted without `force`. Default: `true`. ### done ```typescript theme={null} done(): boolean ``` Whether the utterance has finished (completed or interrupted). ### interrupt ```typescript theme={null} interrupt(opts: { force?: boolean } = {}): void ``` Interrupt the utterance, marking it done and firing last-audio-byte callbacks. Has no effect on a non-interruptible utterance unless `force` is `true`. ### markDone ```typescript theme={null} markDone(): void ``` Mark the utterance as completed normally, firing last-audio-byte callbacks. ### onLastAudioByte ```typescript theme={null} onLastAudioByte(cb: () => any): () => any ``` Register a callback that fires when the utterance's final audio byte has played. If the utterance is already done, the callback runs immediately; otherwise it is queued and fires once when the utterance finishes. Returns the same callback you passed in. Errors thrown by the callback are caught and logged, never propagated. ### then ```typescript theme={null} then(onfulfilled?: ((value: void) => TResult1 | PromiseLike) | null, onrejected?: ((reason: any) => TResult2 | PromiseLike) | null): Promise ``` Makes the handle awaitable; resolves when the utterance finishes. ### wait ```typescript theme={null} wait(): Promise ``` Returns a promise that resolves when the utterance finishes.