Pydantic AI

Pydantic AI's OpenAI chat model takes a provider with a base URL and a key. That provider is all OpenCheap needs.

What you need

Base URLhttps://api.opencheap.si/v1
API keyA kl_live_… key from the console, kept in OPENCHEAP_API_KEY.
ModelAn id from Models, for example claude-sonnet-5.

terminal

pip install "pydantic-ai-slim[openai]"

An agent with a tool

agent.py

import os
from pydantic_ai import Agent
from pydantic_ai.models.openai import OpenAIChatModel
from pydantic_ai.providers.openai import OpenAIProvider

model = OpenAIChatModel(
    "claude-sonnet-5",
    provider=OpenAIProvider(base_url="https://api.opencheap.si/v1", api_key=os.environ["OPENCHEAP_API_KEY"]),
)
agent = Agent(model, instructions="Answer in one sentence.")


@agent.tool_plain
def get_weather(city: str) -> str:
    """Get the weather for a city."""
    return f"Sunny in {city}"


print(agent.run_sync("What's the weather in Paris?").output)

OpenAIChatModel uses /chat/completions, so any chat model from the Models page works; pick one that supports tool calls when the agent has tools.

What was checked

Run on October 28, 2026 with pydantic-ai-slim 2.31.1 on claude-sonnet-5: the agent called get_weather and answered from its result.

All integrations

Every tool with a setup page.

Models

The ids to use, their prices and context lengths.

Streaming

The events and the usage chunk a tool reads.

Errors

Every code, and which ones to retry.