BidiAgent [Experimental]

BidiAgent [Experimental]

{{ experimental_feature_warning() }}

The BidiAgent is a specialized agent designed for real-time bidirectional streaming conversations. Unlike the standard Agent that follows a request-response pattern, BidiAgent maintains persistent connections that enable continuous audio and text streaming, real-time interruptions, and concurrent tool execution.

flowchart TB
    subgraph User
        A[Microphone] --> B[Audio Input]
        C[Text Input] --> D[Input Events]
        B --> D
    end
    
    subgraph BidiAgent
        D --> E[Agent Loop]
        E --> F[Model Connection]
        F --> G[Tool Execution]
        G --> F
        F --> H[Output Events]
    end
    
    subgraph Output
        H --> I[Audio Output]
        H --> J[Text Output]
        I --> K[Speakers]
        J --> L[Console/UI]
    end

Agent vs BidiAgent

While both Agent and BidiAgent share the same core purpose of enabling AI-powered interactions, they differ significantly in their architecture and use cases.

Standard Agent (Request-Response)

The standard Agent follows a traditional request-response pattern:

from strands import Agent
from strands_tools import calculator

agent = Agent(tools=[calculator])

# Single request-response cycle
result = agent("Calculate 25 * 48")
print(result.message)  # "The result is 1200"

Characteristics:

• Synchronous interaction: One request, one response
• Discrete cycles: Each invocation is independent
• Message-based: Operates on complete messages
• Tool execution: Sequential, blocking the response

BidiAgent (Bidirectional Streaming)

BidiAgent maintains a persistent, bidirectional connection:

import asyncio
from strands.experimental.bidi import BidiAgent, BidiAudioIO
from strands.experimental.bidi.models import BidiNovaSonicModel

model = BidiNovaSonicModel()
agent = BidiAgent(model=model, tools=[calculator])
audio_io = BidiAudioIO()

async def main():
    # Persistent connection with continuous streaming
    await agent.run(
        inputs=[audio_io.input()],
        outputs=[audio_io.output()]
    )

asyncio.run(main())

Characteristics:

• Asynchronous streaming: Continuous input/output
• Persistent connection: Single connection for multiple turns
• Event-based: Operates on streaming events
• Tool execution: Concurrent, non-blocking

When to Use Each

Use Agent when:

• Building chatbots or CLI applications
• Processing discrete requests
• Implementing API endpoints
• Working with text-only interactions
• Simplicity is preferred

Use BidiAgent when:

• Building voice assistants
• Requiring real-time audio streaming
• Needing natural conversation interruptions
• Implementing live transcription
• Building interactive, multi-modal applications

The Bidirectional Agent Loop

The bidirectional agent loop is fundamentally different from the standard agent loop. Instead of processing discrete messages, it continuously streams events in both directions while managing connection state and concurrent operations.

Architecture Overview

flowchart TB
    A[Agent Start] --> B[Model Connection]
    B --> C[Agent Loop]
    C --> D[Model Task]
    C --> E[Event Queue]
    D --> E
    E --> F[receive]
    D --> G[Tool Detection]
    G --> H[Tool Tasks]
    H --> E
    F --> I[User Code]
    I --> J[send]
    J --> K[Model]
    K --> D

Event Flow

Startup Sequence

Agent Initialization

agent = BidiAgent(model=model, tools=[calculator])

Creates tool registry, initializes agent state, and sets up hook registry.

Connection Start

await agent.start()

Calls model.start(system_prompt, tools, messages), establishes WebSocket/SDK connection, sends conversation history if provided, spawns background task for model communication, and enables sending capability.

Event Processing

async for event in agent.receive():
    # Process events

Dequeues events from internal queue, yields to user code, and continues until stopped.

Tool Execution

Tools execute concurrently without blocking the conversation. When a tool is invoked:

1. The tool executor streams events as the tool runs
2. Tool events are queued to the event loop
3. Tool use and result messages are added atomically to conversation history
4. Results are automatically sent back to the model

The special stop_conversation tool triggers agent shutdown instead of sending results back to the model.

Connection Lifecycle

Normal Operation

User → send() → Model → receive() → Model Task → Event Queue → receive() → User
                  ↓
              Tool Use
                  ↓
            Tool Task → Event Queue → receive() → User
                  ↓
            Tool Result → Model

Configuration

BidiAgent supports extensive configuration to customize behavior for your specific use case.

Basic Configuration

from strands.experimental.bidi import BidiAgent
from strands.experimental.bidi.models import BidiNovaSonicModel

model = BidiNovaSonicModel()

agent = BidiAgent(
    model=model,
    tools=[calculator, weather],
    system_prompt="You are a helpful voice assistant.",
    messages=[],  # Optional conversation history
    agent_id="voice_assistant_1",
    name="Voice Assistant",
    description="A voice-enabled AI assistant"
)

Model Configuration

Each model provider has specific configuration options:

from strands.experimental.bidi.models import BidiNovaSonicModel

model = BidiNovaSonicModel(
    model_id="amazon.nova-sonic-v1:0",
    provider_config={
        "audio": {
            "input_rate": 16000,
            "output_rate": 16000,
            "voice": "matthew",  # or "ruth"
            "channels": 1,
            "format": "pcm"
        }
    },
    client_config={
        "boto_session": boto3.Session(),
        "region": "us-east-1"
    }
)

See Model Providers for provider-specific options.

BidiAgent supports many of the same constructs as Agent:

• Tools: Function calling works identically
• Hooks: Lifecycle event handling with bidirectional-specific events
• Session Management: Conversation persistence across sessions
• Tool Executors: Concurrent and custom execution patterns

Lifecycle Management

Understanding the BidiAgent lifecycle is crucial for proper resource management and error handling.

Lifecycle States

stateDiagram-v2
    [*] --> Created: BidiAgent
    Created --> Started: start
    Started --> Running: run or receive
    Running --> Running: send and receive events
    Running --> Stopped: stop
    Stopped --> [*]
    
    Running --> Restarting: Timeout
    Restarting --> Running: Reconnected

State Transitions

1. Creation

agent = BidiAgent(model=model, tools=[calculator])
# Tool registry initialized, agent state created, hooks registered
# NOT connected to model yet

2. Starting

await agent.start(invocation_state={...})
# Model connection established, conversation history sent
# Background tasks spawned, ready to send/receive

3. Running

# Option A: Using run()
await agent.run(inputs=[...], outputs=[...])

# Option B: Manual send/receive
await agent.send("Hello")
async for event in agent.receive():
    # Process events - events streaming, tools executing, messages accumulating
    pass

4. Stopping

await agent.stop()
# Background tasks cancelled, model connection closed, resources cleaned up

Lifecycle Patterns

Using run()

agent = BidiAgent(model=model)
audio_io = BidiAudioIO()

await agent.run(
    inputs=[audio_io.input()],
    outputs=[audio_io.output()]
)

Simplest for I/O-based applications - handles start/stop automatically.

Context Manager

agent = BidiAgent(model=model)

async with agent:
    await agent.send("Hello")
    async for event in agent.receive():
        if isinstance(event, BidiResponseCompleteEvent):
            break

Automatic start() and stop() with exception-safe cleanup. To pass invocation_state, call start() manually before entering the context.

Manual Lifecycle

agent = BidiAgent(model=model)

try:
    await agent.start()
    await agent.send("Hello")
    
    async for event in agent.receive():
        if isinstance(event, BidiResponseCompleteEvent):
            break
finally:
    await agent.stop()

Explicit control with custom error handling and flexible timing.

Connection Restart

When a model times out, the agent automatically restarts:

async for event in agent.receive():
    if isinstance(event, BidiConnectionRestartEvent):
        print("Reconnecting...")
        # Connection restarting automatically
        # Conversation history preserved
        # Continue processing events normally

The restart process: Timeout detected → BidiConnectionRestartEvent emitted → Sending blocked → Hooks invoked → Model restarted with history → New receiver task spawned → Sending unblocked → Conversation continues seamlessly.

Error Handling

Handling Errors in Events

async for event in agent.receive():
    if isinstance(event, BidiErrorEvent):
        print(f"Error: {event.message}")
        # Access original exception
        original_error = event.error
        # Decide whether to continue or break
        break

Handling Connection Errors

try:
    await agent.start()
    async for event in agent.receive():
        # Handle connection restart events
        if isinstance(event, BidiConnectionRestartEvent):
            print("Connection restarting, please wait...")
            continue  # Connection restarts automatically
        
        # Process other events
        pass
except Exception as e:
    print(f"Unexpected error: {e}")
finally:
    await agent.stop()

Note: Connection timeouts are handled automatically. The agent emits BidiConnectionRestartEvent when reconnecting.

Graceful Shutdown

import signal

agent = BidiAgent(model=model)
audio_io = BidiAudioIO()

async def main():
    # Setup signal handler
    loop = asyncio.get_event_loop()
    
    def signal_handler():
        print("\nShutting down gracefully...")
        loop.create_task(agent.stop())
    
    loop.add_signal_handler(signal.SIGINT, signal_handler)
    loop.add_signal_handler(signal.SIGTERM, signal_handler)
    
    try:
        await agent.run(
            inputs=[audio_io.input()],
            outputs=[audio_io.output()]
        )
    except asyncio.CancelledError:
        print("Agent stopped")

asyncio.run(main())

Resource Cleanup

The agent automatically cleans up background tasks, model connections, I/O channels, event queues, and invokes cleanup hooks.

Best Practices

1. Always Use try/finally: Ensure stop() is called even on errors
2. Prefer Context Managers: Use async with for automatic cleanup
3. Handle Restarts Gracefully: Don't treat BidiConnectionRestartEvent as an error
4. Monitor Lifecycle Hooks: Use hooks to track state transitions
5. Test Shutdown: Verify cleanup works under various conditions
6. Avoid Calling stop() During receive(): Only call stop() after exiting the receive loop

Next Steps

• Events - Complete guide to bidirectional streaming events
• I/O Channels - Building custom input/output channels
• Model Providers - Provider-specific configuration
• Quickstart - Getting started guide
• API Reference - Complete API documentation