LangGraph

State-machine agents with graph nodes

LangGraph

LangGraph does not connect to a model provider by itself. Configure a Radium-backed ChatOpenAI model and call it from your graph nodes.

Before you start

You need Python 3.10 or newer, a Radium API key, and a terminal or PowerShell window.

1. Create a project and install the packages

macOS or Linux

mkdir radium-langgraph && cd radium-langgraph
python3 -m venv .venv
source .venv/bin/activate
python -m pip install langgraph langchain-openai

2. Set your Radium credentials

macOS or Linux

export RADIUM_API_KEY="your-radium-api-key"
export RADIUM_MODEL="hal-1.0"

3. Create main.py

import os
from langchain_openai import ChatOpenAI
from langgraph.graph import END, START, MessagesState, StateGraph

api_key = os.getenv("RADIUM_API_KEY")
if not api_key:
    raise SystemExit("Set RADIUM_API_KEY before running this program.")

llm = ChatOpenAI(
    model=os.getenv("RADIUM_MODEL", "hal-1.0"),
    api_key=api_key,
    base_url="https://api.radium.cloud/v1",
    max_tokens=512,
    temperature=0,
    timeout=90,
    max_retries=0,
)

def call_radium(state: MessagesState):
    return {"messages": [llm.invoke(state["messages"])]}

builder = StateGraph(MessagesState)
builder.add_node("call_radium", call_radium)
builder.add_edge(START, "call_radium")
builder.add_edge("call_radium", END)
graph = builder.compile()

result = graph.invoke(
    {
        "messages": [
            {"role": "system", "content": "Follow the user's instruction exactly."},
            {"role": "user", "content": "Reply with exactly: Radium connected."},
        ]
    }
)

content = result["messages"][-1].content
if not content or not str(content).strip():
    raise RuntimeError("Radium returned no visible text.")
print(f"RADIUM_RESPONSE: {str(content).strip()}")

4. Run it

python main.py

Expected output:

RADIUM_RESPONSE: Radium connected.

Choose a model

export RADIUM_MODEL="tycho-1.0"  # or hal-1.0 or clarke-1.0
python main.py

Migrate an existing graph

Replace the model used inside your existing nodes:

llm = ChatOpenAI(
    model="hal-1.0",
    api_key=os.environ["RADIUM_API_KEY"],
    base_url="https://api.radium.cloud/v1",
    max_tokens=512,
)

Your state schema, nodes, edges, routing, and checkpoints do not need to change.

Troubleshooting

Problem	Fix
Authentication errors	Check the API key in the active terminal
404	Use the exact base URL and one of the three listed model IDs
State errors	Make sure the graph node returns a messages list
Import errors	Activate .venv and rerun the installation command

Validation

These instructions were verified with Python 3.12.7, langgraph==1.2.11, and langchain-openai==1.6.0 on August 20, 2026. You do not need those exact package versions.

Text generation and an agent tool loop passed with hal-1.0, clarke-1.0, and tycho-1.0.

Next steps

API quickstart

Call Radium directly

Tool calling

The tool_use and tool_result contract