Use PydanticAI with Radium

PydanticAI supports custom OpenAI-compatible providers. Construct an 
OpenAIChatModel explicitly so requests use Radium's Chat Completions endpoint.
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 PydanticAI
macOS or Linux:
mkdir radium-pydanticai
cd radium-pydanticai
python3 -m venv .venv
source .venv/bin/activate
python -m pip install "pydantic-ai-slim[openai]"
Windows PowerShell:
mkdir radium-pydanticai
cd radium-pydanticai
py -m venv .venv
.venv\Scripts\Activate.ps1
python -m pip install "pydantic-ai-slim[openai]"
2. Set your Radium credentials
macOS or Linux:
export RADIUM_API_KEY="your-radium-api-key"
export RADIUM_MODEL="hal-1.0"
Windows PowerShell:
$env:RADIUM_API_KEY = "your-radium-api-key"
$env:RADIUM_MODEL = "hal-1.0"
3. Create 
main.py
import os
from pydantic_ai import Agent
from pydantic_ai.models.openai import OpenAIChatModel
from pydantic_ai.providers.openai import OpenAIProvider
api_key = os.getenv("RADIUM_API_KEY")
if not api_key:
    raise SystemExit("Set RADIUM_API_KEY before running this program.")
model = OpenAIChatModel(
    os.getenv("RADIUM_MODEL", "hal-1.0"),
    provider=OpenAIProvider(
        api_key=api_key,
        base_url="https://api.radium.cloud/v1",
    ),
)
agent = Agent(
    model,
    system_prompt="Follow the user's instruction exactly.",
    model_settings={"max_tokens": 512, "temperature": 0},
)
result = agent.run_sync("Reply with exactly: Radium connected.")
if not result.output or not str(result.output).strip():
    raise RuntimeError("Radium returned no visible text.")
print(f"RADIUM_RESPONSE: {str(result.output).strip()}")
Do not use the shorthand 
openai:hal-1.0. Constructing 
OpenAIChatModel explicitly ensures PydanticAI uses the custom Radium provider and Chat Completions endpoint.
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 PydanticAI agent
Replace its model/provider configuration:
model = OpenAIChatModel(
    "hal-1.0",
    provider=OpenAIProvider(
        api_key=os.environ["RADIUM_API_KEY"],
        base_url="https://api.radium.cloud/v1",
    ),
)
agent = Agent(model)
Your system prompts, dependency types, tools, and output types can remain unchanged.
Troubleshooting
Authentication errors: set the key in the terminal running Python.
Calls going to OpenAI instead of Radium: use the explicit 
OpenAIProvider construction shown above.
404: verify 
/v1 and the exact model name.
Empty output: keep the output allowance at 512 or higher.
Validation
Version note: these instructions were verified with Python 3.12.7 and 
pydantic-ai-slim[openai]==2.31.1 on August 20, 2026. You do not need that exact package version. Text generation and 
tool_plain execution passed with 
hal-1.0, 
clarke-1.0, and 
tycho-1.0.
Reference: PydanticAI OpenAI-compatible models.
Next
API quickstart, for calling Radium directly
Tool calling, for the 
tool_use and 
tool_result contract