### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

I am using LiteLLM to handle an LLM endpoint (specifically, it is an OpenAI API).

I have made a Pydantic AI agent, and want to stream a response using the [Agent-User Interaction (AG-UI)](https://pydantic.dev/docs/ai/integrations/ui/ag-ui/) Protocol.

However, I get an error when trying to use LiteLLM: ``` Can't instantiate abstract class LiteLLMStreamedResponse without an implementation for abstract method 'provider_url' ```

I know I can switch to a OpenAI API client, and when I do I have no problems.

### Steps to Reproduce

1. Create LiteLLM model ``` from pydantic_ai_litellm import LiteLLMModel

model = LiteLLMModel( model_name, api_base, api_key, custom_llm_provider, ) ``` 2. Create PydanticAI Agent ``` from pydantic_ai import Agent

agent = Agent( model, instructions='You always respond in Italian.' ) ``` 3. Create FastAPI app ``` from fastapi import FastAPI from fastapi.requests import Request from fastapi.responses import Response from pydantic_ai.ui.ag_ui import AGUIAdapter

app = FastAPI(title="Pydantic Agen…