---
library_name: transformers
license: apache-2.0
base_model: Qwen/Qwen3-4B-Instruct-2507
tags:
  - tool-use
  - multi-turn
  - agents
  - grpo
  - reinforcement-learning
  - tau2-bench
datasets:
  - Jarrodbarnes/tau2-sft-seed-v3
pipeline_tag: text-generation
model-index:
  - name: Qwen3-4B-tau2-grpo-v1
    results:
      - task:
          type: multi-turn-tool-use
          name: tau2-bench
        dataset:
          type: tau2-bench
          name: tau2-bench (test split)
        metrics:
          - type: pass@1
            value: 36.0
            name: Pass@1 (Overall)
          - type: pass@4
            value: 59.0
            name: Pass@4 (Overall)
---

# Qwen3-4B-tau2-grpo-v1

A 4B parameter model fine-tuned for multi-turn tool-use tasks, achieving **59% Pass@4** on tau2-bench (test split). This represents a **4x improvement** over the base model and demonstrates that progressive training (SFT -> RFT -> GRPO) works effectively for complex, multi-turn agent tasks.

## Model Description

This model was trained using a three-stage pipeline:
1. **SFT (Supervised Fine-Tuning)**: Learning protocol and tool schemas from successful trajectories
2. **RFT (Rejection Fine-Tuning)**: Concentrating training on high-quality rollouts via rejection sampling
3. **GRPO (Group Relative Policy Optimization)**: Reinforcement learning with turn-level reward shaping

The training process is documented in the [tau2 training cookbook](https://github.com/THUDM/slime/blob/main/examples/tau-bench/training_cookbook.md).

## Performance

### tau2-bench Test Split (Pass@4 evaluation)

| Domain | Pass@1 | Pass@4 | Tasks |
|--------|--------|--------|-------|
| **Overall** | **36.0%** | **59.0%** | 100 |
| Airline | 15.0% | 45.0% | 20 |
| Retail | 55.0% | 85.0% | 40 |
| Telecom | 27.5% | 40.0% | 40 |

### Training Progression

| Stage | Overall Pass@4 |
|-------|----------------|
| Baseline (Qwen3-4B-Instruct) | 14.3% |
| SFT + RFT | 27.0% |
| GRPO (this model) | **59.0%** |

**Eval config**: `temperature=0.8`, `top_p=1.0`, `top_k=20`, `num_samples=4`, `TAU2_USER_MODEL=gpt-4.1-mini`, `TAU2_USER_TEMPERATURE=0.7`, `TAU2_MAX_STEPS=100`.

## Usage

### With SGLang (recommended for evaluation)

```bash
# Start the server (use --tp 1 for single GPU)
python -m sglang.launch_server \
  --model-path Jarrodbarnes/Qwen3-4B-tau2-grpo-v1 \
  --host 0.0.0.0 --port 30000 --tp 2 --mem-fraction-static 0.70
```

### With Transformers

```python
from transformers import AutoModelForCausalLM, AutoTokenizer

model_name = "Jarrodbarnes/Qwen3-4B-tau2-grpo-v1"
tokenizer = AutoTokenizer.from_pretrained(model_name)
model = AutoModelForCausalLM.from_pretrained(
    model_name,
    torch_dtype="auto",
    device_map="auto"
)
```

### Function Calling Format

This model uses Qwen3 native function calling format:

```
<tool_call>{"name": "tool_name", "arguments": {"arg": "value"}}</tool_call>
```

Include `</tool_call>` in stop sequences for proper parsing.

## Training Details

- **Base model**: [Qwen/Qwen3-4B-Instruct-2507](https://huggingface.co/Qwen/Qwen3-4B-Instruct-2507)
- **Training framework**: [SLIME](https://github.com/THUDM/slime) (Megatron-LM + SGLang)
- **SFT data**: [tau2-sft-seed-v3](https://huggingface.co/datasets/Jarrodbarnes/tau2-sft-seed-v3)
- **GRPO steps**: 21 optimizer steps
- **Reward shaping**: Turn-level partial scores from tau2-bench reward_info
- **User simulator (training)**: Local Qwen3-4B-Instruct on port 30001
- **User simulator (eval)**: GPT-4.1-mini via OpenAI API

### W&B Training Logs

- SFT run: [b7d80rfe](https://wandb.ai/jbarnes850-near-protocol/tau2-cookbook/runs/b7d80rfe)
- GRPO run: [pkeu9kck](https://wandb.ai/jbarnes850-near-protocol/tau2-cookbook/runs/pkeu9kck)

## Resources

- [Training Cookbook](https://github.com/THUDM/slime/blob/main/examples/tau-bench/training_cookbook.md) - Full methodology and reproduction steps
- [SFT Checkpoint](https://huggingface.co/Jarrodbarnes/Qwen3-4B-tau2-sft1) - Intermediate SFT+RFT checkpoint
- [Training Dataset](https://huggingface.co/datasets/Jarrodbarnes/tau2-sft-seed-v3) - Filtered RFT trajectories
- [tau2-bench](https://github.com/sierra-research/tau2-bench) - Benchmark repository

## Limitations

- **Telecom domain**: Dual-control tasks (where the agent must instruct rather than execute) remain challenging (40% Pass@4)
- **User simulator sensitivity**: Results vary with user simulator choice; GPT-4.1-mini recommended for reproducibility
- **Pass@k vs Pass^k**: This model reports pass@k (any success in k attempts), not the pass^k metric used on the official tau2-bench leaderboard

## Citation

```bibtex
@misc{qwen3-tau2-grpo,
  title={Qwen3-4B-tau2-grpo-v1: Multi-Turn Tool-Use Agent via Progressive RL Training},
  author={Jarrod Barnes},
  year={2025},
  url={https://huggingface.co/Jarrodbarnes/Qwen3-4B-tau2-grpo-v1}
}
```

## Acknowledgments

- [Qwen Team](https://github.com/QwenLM/Qwen3) for the base model
- [Sierra Research](https://github.com/sierra-research/tau2-bench) for tau2-bench
- [THUDM](https://github.com/THUDM/slime) for the SLIME training framework