adk-realtime

Real-time bidirectional audio streaming for Rust Agent Development Kit (ADK-Rust) agents.

Overview

adk-realtime provides a unified interface for building voice-enabled AI agents using real-time streaming APIs. It follows the OpenAI Agents SDK pattern with a separate, decoupled implementation that integrates seamlessly with the ADK agent ecosystem.

Features

• RealtimeAgent — Implements adk_core::Agent with full callback/tool/instruction support
• Multiple Providers — OpenAI Realtime API, Gemini Live API, Vertex AI Live API
• Multiple Transports — WebSocket, WebRTC (OpenAI), LiveKit bridge
• Audio Streaming — Bidirectional audio with PCM16, G711, Opus formats
• Voice Activity Detection — Server-side VAD for natural conversation flow
• Tool Calling — Real-time function/tool execution during voice conversations
• Agent Handoff — Transfer between agents using sub_agents
• Feature Flags — Pay only for what you use; all transports are opt-in

Architecture

              ┌─────────────────────────────────────────┐
              │              Agent Trait                 │
              │  (name, description, run, sub_agents)    │
              └────────────────┬────────────────────────┘
                               │
       ┌───────────────────────┼───────────────────────┐
       │                       │                       │
┌──────▼──────┐      ┌─────────▼─────────┐   ┌─────────▼─────────┐
│  LlmAgent   │      │  RealtimeAgent    │   │  SequentialAgent  │
│ (text-based) │      │  (voice-based)    │   │   (workflow)      │
└─────────────┘      └───────────────────┘   └───────────────────┘

Transport Layer

┌──────────────────────────────────────────────────────────────┐
│                    RealtimeSession trait                      │
├──────────────┬──────────────┬──────────────┬─────────────────┤
│ OpenAI WS    │ OpenAI WebRTC│ Gemini Live  │ Vertex AI Live  │
│ (openai)     │ (openai-     │ (gemini)     │ (vertex-live)   │
│              │  webrtc)     │              │                 │
└──────────────┴──────────────┴──────────────┴─────────────────┘

┌──────────────────────────────────────────────────────────────┐
│              LiveKit WebRTC Bridge (livekit)                  │
│  LiveKitEventHandler · bridge_input · bridge_gemini_input    │
└──────────────────────────────────────────────────────────────┘

Supported Providers & Transports

Quick Start

Add to your Cargo.toml:

[dependencies]
adk-realtime = { version = "0.3", features = ["openai"] }

Using RealtimeAgent (Recommended)

use adk_realtime::{RealtimeAgent, openai::OpenAIRealtimeModel};
use std::sync::Arc;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let api_key = std::env::var("OPENAI_API_KEY")?;
    let model = Arc::new(OpenAIRealtimeModel::new(&api_key, "gpt-4o-realtime-preview-2024-12-17"));

    let agent = RealtimeAgent::builder("voice_assistant")
        .model(model)
        .instruction("You are a helpful voice assistant.")
        .voice("alloy")
        .server_vad()
        .build()?;

    // RealtimeAgent implements the Agent trait — use with ADK runner
    Ok(())
}

Using Low-Level Session API

use adk_realtime::{RealtimeModel, RealtimeConfig, ServerEvent};
use adk_realtime::openai::OpenAIRealtimeModel;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let model = OpenAIRealtimeModel::new(
        std::env::var("OPENAI_API_KEY")?,
        "gpt-4o-realtime-preview-2024-12-17",
    );

    let config = RealtimeConfig::default()
        .with_instruction("You are a helpful voice assistant.")
        .with_voice("alloy");

    let session = model.connect(config).await?;
    session.send_text("Hello!").await?;
    session.create_response().await?;

    while let Some(event) = session.next_event().await {
        match event? {
            ServerEvent::AudioDelta { delta, .. } => { /* play audio */ }
            ServerEvent::TextDelta { delta, .. } => print!("{}", delta),
            _ => {}
        }
    }
    Ok(())
}

Transport Guides

Vertex AI Live

Connect to Gemini Live API via Vertex AI with Application Default Credentials:

adk-realtime = { version = "0.3", features = ["vertex-live"] }

use adk_realtime::gemini::{GeminiLiveBackend, GeminiRealtimeModel};

// Convenience constructor — auto-discovers ADC credentials
let backend = GeminiLiveBackend::vertex_adc("my-project", "us-central1")?;

// Or manual credentials construction
let credentials = google_cloud_auth::credentials::Credentials::default().await?;
let backend = GeminiLiveBackend::Vertex {
    credentials,
    region: "us-central1".into(),
    project_id: std::env::var("GOOGLE_CLOUD_PROJECT")?,
};

let model = GeminiRealtimeModel::new(backend, "models/gemini-live-2.5-flash-native-audio");
let session = model.connect(config).await?;

Prerequisites:

• Google Cloud project with Vertex AI API enabled
• ADC configured (gcloud auth application-default login)

OpenAI WebRTC

Lower-latency audio transport using Sans-IO WebRTC with Opus codec:

adk-realtime = { version = "0.3", features = ["openai-webrtc"] }

use adk_realtime::openai::{OpenAIRealtimeModel, OpenAITransport};

let model = OpenAIRealtimeModel::new(api_key, "gpt-4o-realtime-preview-2024-12-17")
    .with_transport(OpenAITransport::WebRTC);
let session = model.connect(config).await?;

Build requirement: cmake must be installed (the audiopus crate builds the Opus C library from source). With cmake >= 4.0, set the environment variable:

export CMAKE_POLICY_VERSION_MINIMUM=3.5

LiveKit WebRTC Bridge

Bridge any EventHandler to a LiveKit room for production voice apps:

adk-realtime = { version = "0.3", features = ["livekit", "openai"] }

use adk_realtime::livekit::{LiveKitEventHandler, bridge_input};

// Wrap your event handler to publish model audio to LiveKit
let lk_handler = LiveKitEventHandler::new(inner_handler, audio_source, 24000, 1);

// Bridge participant audio from LiveKit into the RealtimeRunner
tokio::spawn(bridge_input(remote_track, runner));

For Gemini's 16 kHz format, use bridge_gemini_input instead.

Feature Flags

Default features: none. You opt in to exactly what you need.

Feature Flag Dependency Graph

vertex-live  ──► gemini + google-cloud-auth
openai-webrtc ──► openai + str0m + audiopus + reqwest
livekit      ──► livekit + livekit-api
full         ──► openai + gemini + vertex-live + livekit
full-webrtc  ──► full + openai-webrtc

RealtimeAgent Features

Shared with LlmAgent

Realtime-Specific

Event Types

Server Events

Client Events

Audio Formats

Error Types

Transport-specific error variants with actionable context:

Examples

# Vertex AI Live voice assistant (requires ADC + GCP project)
cargo run --example vertex_live_voice --features vertex-live

# LiveKit bridge with OpenAI model (requires LiveKit server)
cargo run --example livekit_bridge --features "livekit,openai"

# OpenAI WebRTC low-latency session (requires cmake + API key)
CMAKE_POLICY_VERSION_MINIMUM=3.5 cargo run --example openai_webrtc --features openai-webrtc

Testing

# Property tests (no credentials needed)
cargo test -p adk-realtime --test error_context_tests
cargo test -p adk-realtime --features vertex-live --test vertex_url_property_tests
cargo test -p adk-realtime --features livekit --test livekit_delegation_tests
CMAKE_POLICY_VERSION_MINIMUM=3.5 cargo test -p adk-realtime --features openai-webrtc --test opus_roundtrip_tests
CMAKE_POLICY_VERSION_MINIMUM=3.5 cargo test -p adk-realtime --features openai-webrtc --test sdp_offer_tests

# All features
CMAKE_POLICY_VERSION_MINIMUM=3.5 cargo test -p adk-realtime --features full

# Integration tests (require real credentials, marked #[ignore])
cargo test -p adk-realtime --features vertex-live -- --ignored

Compilation Verification

cargo check -p adk-realtime                          # default (no deps)
cargo check -p adk-realtime --features openai        # OpenAI WebSocket
cargo check -p adk-realtime --features gemini        # Gemini Live
cargo check -p adk-realtime --features vertex-live   # Vertex AI Live
cargo check -p adk-realtime --features livekit       # LiveKit bridge
CMAKE_POLICY_VERSION_MINIMUM=3.5 \
  cargo check -p adk-realtime --features openai-webrtc  # OpenAI WebRTC
CMAKE_POLICY_VERSION_MINIMUM=3.5 \
  cargo check -p adk-realtime --features full            # everything

Feature Flags

Vertex AI Live

Connect to Gemini via Vertex AI with Application Default Credentials:

use adk_realtime::gemini::{GeminiLiveBackend, GeminiLiveModel, build_vertex_live_url};

// Uses ADC — no API key needed, just `gcloud auth application-default login`
let model = GeminiLiveModel::new(GeminiLiveBackend::Vertex {
    project_id: "my-project".into(),
    region: "us-central1".into(),
    model: "gemini-live-2.5-flash-native-audio".into(),
});

Feature Flag Graph

vertex-live  → gemini + google-cloud-auth
livekit      → livekit + livekit-api
openai-webrtc → openai + str0m + audiopus (requires cmake)
full         → openai + gemini + vertex-live + livekit
full-webrtc  → full + openai-webrtc

## License

Apache-2.0

## Part of ADK-Rust

This crate is part of the [ADK-Rust](https://github.com/zavora-ai/adk-rust) framework for building AI agents in Rust.