Async

Overview

Async provides high-quality text-to-speech synthesis with two service implementations: AsyncAITTSService (WebSocket-based) for real-time streaming with interruption support, and AsyncAIHttpTTSService (HTTP-based) for simpler synthesis. AsyncAITTSService is recommended for interactive applications requiring low latency.

AsyncAI TTS API Reference

Pipecat’s API methods for AsyncAI TTS integration

Example Implementation

Complete example with WebSocket streaming

Async Documentation

Official Async API documentation

Voice Models

Explore available voice models and features

Installation

To use Async services, install the required dependencies:

uv add "pipecat-ai[asyncai]"

Prerequisites

Async Account Setup

Before using Async TTS services, you need:

Async Account: Sign up at Async
API Key: Generate an API key from your account dashboard
Voice Selection: Choose from available voice models

Required Environment Variables

ASYNCAI_API_KEY: Your Async API key for authentication

Configuration

AsyncAITTSService

str

required

Async API key.

str

required

deprecated

UUID of the voice to use for synthesis. Deprecated in v0.0.105. Use settings=AsyncAITTSService.Settings(voice=...) instead.

str

default:"async_flash_v1.0"

deprecated

TTS model to use. Deprecated in v0.0.105. Use settings=AsyncAITTSService.Settings(model=...) instead.

str

default:"v1"

Async API version.

str

default:"wss://api.async.com/text_to_speech/websocket/ws"

WebSocket endpoint URL.

int

default:"None"

Output audio sample rate in Hz. When None, uses the pipeline’s configured sample rate.

str

default:"pcm_s16le"

Audio encoding format.

str

default:"raw"

Audio container format.

TextAggregationMode

default:"TextAggregationMode.SENTENCE"

Controls how incoming text is aggregated before synthesis. SENTENCE (default) buffers text until sentence boundaries, producing more natural speech. TOKEN streams tokens directly for lower latency. Import from pipecat.services.tts_service.

bool

default:"None"

deprecated

Deprecated in v0.0.104. Use text_aggregation_mode instead.

InputParams

default:"None"

deprecated

Deprecated in v0.0.105. Use settings=AsyncAITTSService.Settings(...) instead.

AsyncAITTSService.Settings

default:"None"

Runtime-configurable settings. See Settings below.

AsyncAIHttpTTSService

The HTTP service accepts similar parameters to the WebSocket service, with these differences:

aiohttp.ClientSession

required

An aiohttp session for HTTP requests. You must create and manage this yourself.

str

default:"https://api.async.com"

HTTP API base URL (instead of WebSocket URL).

Settings

Runtime-configurable settings passed via the settings constructor argument using AsyncAITTSService.Settings(...). These can be updated mid-conversation with TTSUpdateSettingsFrame. See Service Settings for details.

Parameter	Type	Default	Description
`model`	`str`	`None`	Model identifier. (Inherited.)
`voice`	`str`	`None`	Voice identifier. (Inherited.)
`language`	`Language \| str`	`None`	Language for synthesis. (Inherited.)

Usage

Basic Setup

from pipecat.services.asyncai import AsyncAITTSService

tts = AsyncAITTSService(
    api_key=os.getenv("ASYNCAI_API_KEY"),
    settings=AsyncAITTSService.Settings(
        voice="your-voice-uuid",
    ),
)

With Language Customization

from pipecat.transcriptions.language import Language

tts = AsyncAITTSService(
    api_key=os.getenv("ASYNCAI_API_KEY"),
    settings=AsyncAITTSService.Settings(
        voice="your-voice-uuid",
        model="async_flash_v1.0",
        language=Language.ES,
    ),
)

HTTP Service

import aiohttp
from pipecat.services.asyncai import AsyncAIHttpTTSService

async with aiohttp.ClientSession() as session:
    tts = AsyncAIHttpTTSService(
        api_key=os.getenv("ASYNCAI_API_KEY"),
        settings=AsyncAIHttpTTSService.Settings(
            voice="your-voice-uuid",
        ),
        aiohttp_session=session,
    )

The InputParams / params= pattern is deprecated as of v0.0.105. Use Settings / settings= instead. See the Service Settings guide for migration details.

Event Handlers

Async TTS supports the standard service connection events:

Event	Description
`on_connected`	Connected to Async WebSocket
`on_disconnected`	Disconnected from Async WebSocket
`on_connection_error`	WebSocket connection error occurred

@tts.event_handler("on_connected")
async def on_connected(service):
    print("Connected to Async")

Pipecat Server

Client SDKs

Pipecat Flows

Pipecat Cloud

CLI

Pipecat Context Hub

Overview

AsyncAI TTS API Reference

Example Implementation

Async Documentation

Voice Models

Installation

Prerequisites

Async Account Setup

Required Environment Variables

Configuration

AsyncAITTSService

AsyncAIHttpTTSService

Settings

Usage

Basic Setup

With Language Customization

HTTP Service

Event Handlers

​Overview

AsyncAI TTS API Reference

Example Implementation

Async Documentation

Voice Models

​Installation

​Prerequisites

​Async Account Setup

​Required Environment Variables

​Configuration

​AsyncAITTSService

​AsyncAIHttpTTSService

​Settings

​Usage

​Basic Setup

​With Language Customization

​HTTP Service

​Event Handlers

Overview

Installation

Prerequisites

Async Account Setup

Required Environment Variables

Configuration

AsyncAITTSService

AsyncAIHttpTTSService

Settings

Usage

Basic Setup

With Language Customization

HTTP Service

Event Handlers