So yeah, shouldn't be too hard, but Burr does not replace LLM API calls -- you can bring whatever frameworks you want. You could do this by writing a simple function:

    @action(reads=["prompt"], writes=["response"])
    def my_action(state: State) -> Tuple[dict, State]:
       prompt = state["prompt"]
       # you stick in whatever library you want for the call 
       llm_response = whatever_library(prompt)
       state = state.update(response=llm_response)
       return {"response" : llm_response}, state.update(response=llm_response)

Does this help?