app.py

import gradio as gr
import torch
from transformers import AutoModelForCausalLM, AutoTokenizer

MODEL_NAME = "ValiantLabs/Qwen3-4B-Thinking-2507-Esper3.1"

# Load model & tokenizer once at startup
tokenizer = AutoTokenizer.from_pretrained(MODEL_NAME)
model = AutoModelForCausalLM.from_pretrained(
    MODEL_NAME,
    torch_dtype="auto",
    device_map="auto"
)

def ask_question(prompt):
    """Generate response (thinking + final content) from Qwen3 model."""
    try:
        messages = [{"role": "user", "content": prompt}]
        text = tokenizer.apply_chat_template(
            messages,
            tokenize=False,
            add_generation_prompt=True,
            enable_thinking=True  # thinking mode
        )
        inputs = tokenizer([text], return_tensors="pt").to(model.device)

        generated_ids = model.generate(
            **inputs,
            max_new_tokens=4096,
            temperature=0.7,
            do_sample=True
        )
        output_ids = generated_ids[0][len(inputs.input_ids[0]):].tolist()

        # Find the thinking section (token 151668 == </think>)
        try:
            index = len(output_ids) - output_ids[::-1].index(151668)
        except ValueError:
            index = 0

        thinking_content = tokenizer.decode(output_ids[:index], skip_special_tokens=True).strip("\n")
        content = tokenizer.decode(output_ids[index:], skip_special_tokens=True).strip("\n")

        return thinking_content, content
    except Exception as e:
        return f"⚠️ Error: {e}", ""

# --- Gradio UI ---
with gr.Blocks(title="Qwen3 Thinking Chat") as demo:
    gr.Markdown("## 🧠 Qwen3-4B-Thinking — Ask Anything")
    gr.Markdown(
        "This demo uses **ValiantLabs/Qwen3-4B-Thinking-2507-Esper3.1**, "
        "a reasoning model that shows its internal 'thinking' trace before giving the final answer."
    )

    with gr.Row():
        prompt_box = gr.Textbox(
            label="Ask your question",
            placeholder="e.g. Explain how quantum entanglement works.",
            lines=3
        )

    with gr.Row():
        think_output = gr.Textbox(label="🧩 Thinking process", lines=10)
        final_output = gr.Textbox(label="💬 Final answer", lines=10)

    ask_btn = gr.Button("🚀 Generate Answer")

    ask_btn.click(
        fn=ask_question,
        inputs=prompt_box,
        outputs=[think_output, final_output]
    )

demo.launch()