Multi-agent¶

A single agent might struggle if it needs to specialize in multiple domains or manage many tools. To tackle this, you can break your agent into smaller, independent agents and composing them into a multi-agent system.

In multi-agent systems, agents need to communicate between each other. They do so via handoffs — a primitive that describes which agent to hand control to and the payload to send to that agent.

Two of the most popular multi-agent architectures are:

supervisor — individual agents are coordinated by a central supervisor agent. The supervisor controls all communication flow and task delegation, making decisions about which agent to invoke based on the current context and task requirements.
swarm — agents dynamically hand off control to one another based on their specializations. The system remembers which agent was last active, ensuring that on subsequent interactions, the conversation resumes with that agent.

Supervisor¶

Supervisor

Use langgraph-supervisor library to create a supervisor multi-agent system:

pip install langgraph-supervisor

API Reference: ChatOpenAI | create_react_agent

from langchain_openai import ChatOpenAI
from langgraph.prebuilt import create_react_agent
from langgraph_supervisor import create_supervisor

def book_hotel(hotel_name: str):
    """Book a hotel"""
    return f"Successfully booked a stay at {hotel_name}."

def book_flight(from_airport: str, to_airport: str):
    """Book a flight"""
    return f"Successfully booked a flight from {from_airport} to {to_airport}."

flight_assistant = create_react_agent(
    model="openai:gpt-4o",
    tools=[book_flight],
    prompt="You are a flight booking assistant",
    name="flight_assistant"
)

hotel_assistant = create_react_agent(
    model="openai:gpt-4o",
    tools=[book_hotel],
    prompt="You are a hotel booking assistant",
    name="hotel_assistant"
)

supervisor = create_supervisor(
    agents=[flight_assistant, hotel_assistant],
    model=ChatOpenAI(model="gpt-4o"),
    prompt="You manage a hotel booking assistant and a flight booking assistant. Assign work to them."
).compile()

for chunk in supervisor.stream({
    "messages": "book a flight from BOS to JFK and a stay at McKittrick Hotel"
}):
    print(chunk)
    print("\n")

Swarm¶

Swarm

Use langgraph-swarm library to create a swarm multi-agent system:

pip install langgraph-swarm

API Reference: create_react_agent

from langgraph.prebuilt import create_react_agent
from langgraph_swarm import create_swarm, create_handoff_tool

transfer_to_hotel_assistant = create_handoff_tool(
    agent_name="hotel_assistant",
    description="Transfer user to the hotel-booking assistant.",
)
transfer_to_flight_assistant = create_handoff_tool(
    agent_name="flight_assistant",
    description="Transfer user to the flight-booking assistant.",
)

flight_assistant = create_react_agent(
    model="anthropic:claude-3-5-sonnet-latest",
    tools=[book_flight, transfer_to_hotel_assistant],
    prompt="You are a flight booking assistant",
    name="flight_assistant"
)
hotel_assistant = create_react_agent(
    model="anthropic:claude-3-5-sonnet-latest",
    tools=[book_hotel, transfer_to_flight_assistant],
    prompt="You are a hotel booking assistant",
    name="hotel_assistant"
)

swarm = create_swarm(
    agents=[flight_assistant, hotel_assistant],
    default_active_agent="flight_assistant"
).compile()

for chunk in supervisor.stream({
    "messages": "book a flight from BOS to JFK and a stay at McKittrick Hotel"
}):
    print(chunk)
    print("\n")

Handoffs¶

A common pattern in multi-agent interactions is handoffs, where one agent hands off control to another. Handoffs allow you to specify:

destination: target agent to navigate to
payload: information to pass to that agent

This is used both by langgraph-supervisor (supervisor hands off to individual agents) and langgraph-swarm (an individual agent can hand off to other agents).

To implement handoffs with create_react_agent, you need to:

Create a special tool that can transfer control to a different agent

def transfer_to_bob():
    """Transfer to bob."""
    return Command(
        # name of the agent (node) to go to
        goto="bob",
        # data to send to the agent
        update={"messages": [...]},
        # indicate to LangGraph that we need to navigate to
        # agent node in a parent graph
        graph=Command.PARENT,
    )

Create individual agents that have access to handoff tools:

flight_assistant = create_react_agent(
    ..., tools=[book_flight, transfer_to_hotel_assistant]
)
hotel_assistant = create_react_agent(
    ..., tools=[book_hotel, transfer_to_flight_assistant]
)

Define a parent graph that contains individual agents as nodes:

from langgraph.graph import StateGraph, MessagesState
multi_agent_graph = (
    StateGraph(MessagesState)
    .add_node(flight_assistant)
    .add_node(hotel_assistant)
    ...
)

Putting this together, here is how you can implement a simple multi-agent system with two agents — a flight booking assistant and a hotel booking assistant:

from typing import Annotated
from langchain_core.tools import tool, InjectedToolCallId
from langgraph.prebuilt import create_react_agent, InjectedState
from langgraph.graph import StateGraph, START, MessagesState
from langgraph.types import Command

def create_handoff_tool(*, agent_name: str, description: str | None = None):
    name = f"transfer_to_{agent_name}"
    description = description or f"Transfer to {agent_name}"

    @tool(name, description=description)
    def handoff_tool(
        state: Annotated[MessagesState, InjectedState], # (1)!
        tool_call_id: Annotated[str, InjectedToolCallId],
    ) -> Command:
        tool_message = {
            "role": "tool",
            "content": f"Successfully transferred to {agent_name}",
            "name": name,
            "tool_call_id": tool_call_id,
        }
        return Command(  # (2)!
            goto=agent_name,  # (3)!
            update={"messages": state["messages"] + [tool_message]},  # (4)!
            graph=Command.PARENT,  # (5)!
        )
    return handoff_tool

# Handoffs
transfer_to_hotel_assistant = create_handoff_tool(
    agent_name="hotel_assistant",
    description="Transfer user to the hotel-booking assistant.",
)
transfer_to_flight_assistant = create_handoff_tool(
    agent_name="flight_assistant",
    description="Transfer user to the flight-booking assistant.",
)

# Simple agent tools
def book_hotel(hotel_name: str):
    """Book a hotel"""
    return f"Successfully booked a stay at {hotel_name}."

def book_flight(from_airport: str, to_airport: str):
    """Book a flight"""
    return f"Successfully booked a flight from {from_airport} to {to_airport}."

# Define agents
flight_assistant = create_react_agent(
    model="anthropic:claude-3-5-sonnet-latest",
    tools=[book_flight, transfer_to_hotel_assistant],
    prompt="You are a flight booking assistant",
    name="flight_assistant"
)
hotel_assistant = create_react_agent(
    model="anthropic:claude-3-5-sonnet-latest",
    tools=[book_hotel, transfer_to_flight_assistant],
    prompt="You are a hotel booking assistant",
    name="hotel_assistant"
)

# Define multi-agent graph
multi_agent_graph = (
    StateGraph(MessagesState)
    .add_node(flight_assistant)
    .add_node(hotel_assistant)
    .add_edge(START, "flight_assistant")
    .compile()
)

# Run the multi-agent graph
for chunk in multi_agent_graph.stream({
    "messages": "book a flight from BOS to JFK and a stay at McKittrick Hotel"
}):
    print(chunk)
    print("\n")

Access agent's state
The Command primitive allows specifying a state update and a node transition as a single operation, making it useful for implementing handoffs.
Name of the agent or node to hand off to.
Take the agent's messages and add them to the parent's state as part of the handoff. The next agent will see the parent state.
Indicate to LangGraph that we need to navigate to agent node in a parent multi-agent graph.

Note

This handoff implementation assumes that:

each agent receives overall message history (across all agents) in the multi-agent system as its input
each agent outputs its internal messages history to the overall message history of the multi-agent system

Check out LangGraph supervisor and swarm documentation to learn how to customize handoffs.

Multi-agent¶

Supervisor¶

Swarm¶

Handoffs¶

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