Cartesia

Cartesia provides low-latency text-to-speech with the Sonic model. Designed for real-time voice applications with natural-sounding speech synthesis.

Vision Agents uses Stream Video for real-time WebRTC transport by default. External WebRTC transports are supported as well. Most AI providers offer free tiers to get started.

Cartesia also provides low-latency speech-to-text. You can use both in the same agent.

Installation

uv add "vision-agents[cartesia]"

Quick Start

from vision_agents.core import Agent, User
from vision_agents.plugins import cartesia, gemini, deepgram, getstream

agent = Agent(
    edge=getstream.Edge(),
    agent_user=User(name="Assistant", id="agent"),
    instructions="You are a helpful assistant.",
    llm=gemini.LLM("gemini-3-flash-preview"),
    stt=deepgram.STT(),
    tts=cartesia.TTS(),
)

Set CARTESIA_API_KEY in your environment or pass api_key directly.

Parameters

Name	Type	Default	Description
model_id	str	"sonic-3.5"	Cartesia TTS model
voice_id	str	"6ccbfb76-1fc6-48f7-b71d-91ac6298247b"	Voice ID
sample_rate	int	16000	Audio sample rate in Hz
api_key	str	None	API key (defaults to CARTESIA_API_KEY env var)

Next Steps

Build a Voice Agent

Get started with voice

Build a Video Agent

Add video processing