OPENAI_API_KEY=your_token_here \
uv run \
  --with "litellm==1.82.0" \
  --with "openai-agents[litellm]==0.11.1" \
  python - <<'PY'
import asyncio
import os

from agents import Agent, ModelSettings, Runner, function_tool
from agents.extensions.models.litellm_model import LitellmModel
from openai.types.shared import Reasoning


@function_tool
async def get_weather(city: str) -> str:
    return f"The weather in {city} is 9C and sunny."


async def main() -> None:
    if not os.getenv("OPENAI_API_KEY"):
        raise SystemExit("OPENAI_API_KEY is required")

    agent = Agent(
        name="Repro Agent",
        instructions=(
            "Answer the question using the get_weather tool."
        ),
        tools=[get_weather],
        model=LitellmModel(model="openai/gpt-5.4"),
        model_settings=ModelSettings(
            tool_choice="required",
            max_tokens=500,
            reasoning=Reasoning(effort="low"),
        ),
    )

    try:
        result = await Runner.run(
            agent,
            "What is the current weather in Tartu?",
        )
        print(result.final_output)
    except Exception as exc:
        print(f"{type(exc).__name__}: {exc}")
        raise


asyncio.run(main())
PY

---

litellm.exceptions.BadRequestError: litellm.BadRequestError: OpenAIException - Function tools with reasoning_effort are not supported for gpt-5.4 in /v1/chat/completions. Please use /v1/responses instead.