StepAudio 3 Realtime

Overview

StepFun offers two ways to build voice conversations. StepAudio 3 Realtime is the current flagship for real-time interaction, with major gains in full-duplex dialogue, think-while-speaking, and Voice Agent capabilities. View more demos.

Feature	Chat Completions API	Realtime API
Connection	HTTP request	Persistent WebSocket
Speech recognition (ASR)	Implement yourself or use a third-party service	Built in; user speech is transcribed automatically
Context management	Maintain the `messages` list yourself	Built in; conversation history managed automatically
Voice activity detection (VAD)	Implement yourself	Built in; user speech detected automatically
Web search	Implement the search interface yourself	Built-in `web_search` tool
Knowledge retrieval	Implement yourself	Built-in `retrieval` tool
Latency	Lower (streaming output)	Very low (bidirectional streaming)
Best for	Offline processing, batch jobs, simple integration	Real-time conversation, voice assistants, customer-service bots

The models below can be accessed through the Chat API and the Realtime API respectively.

Models

Positioning: a full-duplex voice model for real-time interaction
Capabilities: natural human-like interaction, full-duplex dialogue, adaptive reasoning, think-while-speaking, Voice Agent
StepAudio 3 Realtime unifies real-time audio understanding, turn management, reasoning, and tool calling within a single conversation. It recognizes not only what the user says, but also tone, emotion, paralinguistic cues, and ambient sound.
Supports natural interruption, backchannel recognition, and turn-taking coordination: the user and the model can speak at the same time; the model stops promptly when genuinely interrupted, and keeps the conversation coherent through natural pauses or casual backchannels.
Responds quickly to simple questions; for complex tasks, it can adaptively engage in deeper reasoning and reduce perceived latency by thinking while speaking.
The Voice Agent can call tools or run back-end tasks once intent is clear; the conversation continues while a task runs, and the result is woven back in naturally.

stepaudio-3-realtime-preview is the model name used during the free-trial period. When the free trial ends, this preview version will be retired and a formal paid version added. Billing and rate limits follow the Pricing and Rate Limits page.

StepAudio 3 Chat

Positioning: a speech-understanding and dialogue model for the Chat Completions API
Capabilities: speech input, text dialogue, context understanding, tool calling
Accessed through the Chat API; suitable for submitting speech or text turn by turn and receiving text replies.
Shares the Audio 3 series’ voice understanding and reasoning; for streaming audio output and full-duplex interaction, use the Realtime API.

stepaudio-3-chat-preview is the model name used during the free-trial period. When the free trial ends, this preview version will be retired and a formal paid version added. Billing and rate limits follow the Pricing and Rate Limits page.

Business scenarios

With its real-time interaction and emotional understanding, the Realtime API has been adopted across industries:

Smart cockpit: a natural voice interface for in-vehicle systems—information lookup, casual conversation, and safety reminders while driving.
Smart devices: real-time voice interaction for IoT hardware, improving how users interact with their devices.
Social and entertainment: emotional-companion agents for social and entertainment apps.
Smart customer service: highly human-like service that improves efficiency and customer satisfaction.
Financial mediation: neutral, professional communication support in the handling of financial disputes.

Quick start

Realtime API reference

Request format, event fields, and interface details for the Realtime API.

Chat API reference

Submit speech or text and receive text replies over the Chat Completion API.

Realtime API Demo

A reference front-end console for building a real-time voice conversation.

Start

Models

Pricing

Terms and Agreements

StepAudio 3 Realtime

Overview

Models