app.py

import gradio as gr

def chat(messages):
    user_msg = ""
    for m in reversed(messages):
        if m["role"] == "user":
            user_msg = m["content"]
            break

    return {
        "choices": [
            {
                "message": {
                    "role": "assistant",
                    "content": "Echo: " + user_msg
                }
            }
        ]
    }

demo = gr.Interface(
    fn=chat,
    inputs=gr.JSON(),
    outputs=gr.JSON(),
    api_name="chat"
)

demo.launch()