> ## Documentation Index
> Fetch the complete documentation index at: https://docs.radium.cloud/llms.txt
> Use this file to discover all available pages before exploring further.

# LangGraph

> State-machine agents with graph nodes

<Error>
  This page contains an unverified test date marked in <span style="color:red">red</span>. Needs verification (Vijay, Adam, Alex, Product/Legal).
</Error>

# 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

<CodeGroup>
  ```bash macOS or Linux theme={null}
  mkdir radium-langgraph && cd radium-langgraph
  python3 -m venv .venv
  source .venv/bin/activate
  python -m pip install langgraph langchain-openai
  ```

  ```powershell Windows PowerShell theme={null}
  mkdir radium-langgraph; cd radium-langgraph
  py -m venv .venv
  .venv\Scripts\Activate.ps1
  python -m pip install langgraph langchain-openai
  ```
</CodeGroup>

## 2. Set your Radium credentials

<CodeGroup>
  ```bash macOS or Linux theme={null}
  export RADIUM_API_KEY="your-radium-api-key"
  export RADIUM_MODEL="hal-1.0"
  ```

  ```powershell Windows PowerShell theme={null}
  $env:RADIUM_API_KEY = "your-radium-api-key"
  $env:RADIUM_MODEL = "hal-1.0"
  ```
</CodeGroup>

## 3. Create main.py

```python theme={null}
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

```bash theme={null}
python main.py
```

Expected output:

```
RADIUM_RESPONSE: Radium connected.
```

## Choose a model

```bash theme={null}
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:

```python theme={null}
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

<Check>
  These instructions were verified with Python 3.12.7, `langgraph==1.2.11`, and `langchain-openai==1.6.0` on <span style="color:red">August 20, 2026</span>. You do not need those exact package versions.
</Check>

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

## Next steps

<CardGroup cols={2}>
  <Card title="API quickstart" icon="bolt" href="/quickstart">Call Radium directly</Card>
  <Card title="Tool calling" icon="wrench" href="/core-concepts/tool-calling">The tool\_use and tool\_result contract</Card>
</CardGroup>


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