Intended use & scope
- Input: exactly 3 RGB frames in chronological order (oldest โ current)
plus the task text in the user turn.
- Output: a
<think>WORD</think> block followed by one float with three
decimals, e.g. <think>\ncorrect\n</think>\n\n0.374.
- Not a chat model. It only emits the reward-with-reasoning format under the
system prompt below.
Output contract
The model was trained with a fixed system prompt and a strict output
format. Use the same system prompt at inference (system_prompt.txt in this
directory). It instructs:
- Emit exactly one reasoning word inside
<think>...</think>, from this
vocabulary:
correct โ progress on track (reward increasing/holding)
miss โ gripper missed the grasp and reward just dropped
collision โ an unintended collision just dropped the reward
fall โ the held object fell and reward just dropped
smooth โ motion stalled / non-smooth behaviour dropped the reward
failure โ an unclassified failure event just dropped the reward
- Then a single float in
[0.000, 1.000] (three decimals).
Canonical output (note the blank line after </think>):
<think>
correct
</think>
0.374
The user turn must contain the 3 images followed by the task text, in
the same format used during training (<image><image><image>{task}).
Quickstart
Requires transformers>=4.57, qwen_vl_utils>=0.0.14, torch, accelerate.
Tested environment:
Python 3.12, CUDA 12.8, torch==2.8.0+cu128, torchvision==0.23.0+cu128,
transformers==5.2.0, accelerate==1.13.0, qwen-vl-utils==0.0.14.
conda create -n densereward python=3.12 -y
conda activate densereward
pip install torch==2.8.0 torchvision==0.23.0 --index-url https://download.pytorch.org/whl/cu128
pip install "transformers==5.2.0" "accelerate==1.13.0" "qwen-vl-utils==0.0.14" pillow numpy
import re
import torch
from transformers import AutoModelForImageTextToText, AutoProcessor
from qwen_vl_utils import process_vision_info
MODEL_DIR = "densereward/densereward-3frame-thinking"
SYSTEM_PROMPT = open(f"{MODEL_DIR}/system_prompt.txt").read().strip()
model = AutoModelForImageTextToText.from_pretrained(
MODEL_DIR, torch_dtype=torch.bfloat16, device_map="auto"
)
processor = AutoProcessor.from_pretrained(MODEL_DIR)
frames = [
"file:///path/to/frame_t-2.png",
"file:///path/to/frame_t-1.png",
"file:///path/to/frame_t.png",
]
messages = [
{"role": "system", "content": SYSTEM_PROMPT},
{
"role": "user",
"content": [
{"type": "image", "image": frames[0]},
{"type": "image", "image": frames[1]},
{"type": "image", "image": frames[2]},
{"type": "text", "text": "put the black bowl on the plate"},
],
},
]
text = processor.apply_chat_template(
messages, tokenize=False, add_generation_prompt=True
)
image_inputs, video_inputs = process_vision_info(messages)
inputs = processor(
text=[text],
images=image_inputs,
videos=video_inputs,
padding=True,
return_tensors="pt",
).to(model.device)
with torch.no_grad():
out = model.generate(**inputs, max_new_tokens=32, do_sample=False)
gen = out[:, inputs.input_ids.shape[1]:]
raw = processor.batch_decode(gen, skip_special_tokens=True)[0].strip()
print(raw)
word = re.search(r"<think>\s*(\w+)\s*</think>", raw)
reward = re.search(r"</think>\s*([01](?:\.\d+)?)", raw)
print("reason:", word.group(1) if word else None,
"| reward:", float(reward.group(1)) if reward else None)
Notes:
- Provide the 3 frames in chronological order (oldest first, current last).
- Use
max_new_tokens>=32: the output includes the <think> block and the
reward.
- Always guard the parse: clip reward to
[0, 1] and handle malformed output.
About "thinking" here
The <think>WORD</think> block is part of the trained assistant output,
driven by the system prompt and thinking-labelled training data โ it is not
ms-swift's native --enable_thinking mode (enable_thinking was false for this
run). At inference you only need the bundled system prompt; the model produces the
<think>...</think> block itself.
Loading with ms-swift
The release includes a minimal args.json ({model_type: qwen3_vl, swift_version})
so ms-swift's PtEngine / TransformersEngine can auto-detect the model type for
this local directory. Load it as the base model with no adapter; pass the
bundled system prompt and a 3-image user turn.
Compatibility note: ms-swift 4.2.x targets transformers>=4.57,<5. Under a much
newer transformers (e.g. 5.x) the swift template/prompt composition can
misbehave even though weights load fine โ prefer the transformers path above,
or a swift-matched transformers version, for swift-based inference.
License
Apache License 2.0 (see LICENSE). The base model
Qwen/Qwen3-VL-4B-Instruct
is also Apache-2.0. This fine-tune was produced at the University of North
Carolina at Chapel Hill.
Citation
@article{fang2026densereward,
title={DenseReward: Dense Reward Learning via Failure Synthesis for Robotic Manipulation},
author={Fang, Yu and Dong, Wanxi and Liu, Jiaqi and Yang, Yue and Huo, Mingxiao and Mu, Yao and Yao, Huaxiu and Li, Li Erran and Szafir, Daniel and Ding, Mingyu},
journal={arXiv preprint arXiv:2607.13033},
year={2026}
}