SpatialThinker-3B
SpatialThinker-3B is a 3D-aware multimodal large language model (MLLM) trained with reinforcement learning to integrate structured spatial grounding with multi-step reasoning. The model simulates human-like spatial perception by constructing a scene graph of task-relevant objects and spatial relations, and reasoning towards an answer via dense spatial rewards.
Model Description
- Base Model: Qwen2.5-VL-3B-Instruct
- Training: GRPO (Group Relative Policy Optimization) with dense spatial rewards
- Training Data: STVQA-7K (7,587 spatial VQA samples)
- Authors: Hunar Batra, Haoqin Tu, Hardy Chen, Yuanze Lin, Cihang Xie, Ronald Clark
- Institutions: University of Oxford, UC Santa Cruz
Key Features
- Structured Spatial Reasoning: Constructs question-focused scene subgraphs with objects, bounding boxes, and relations
- Dense Spatial Rewards: Multi-objective reward function enforcing format, count, accuracy, and spatial grounding
- 9 Spatial Reasoning Categories: Relations, reach, size, orientation, instance location, depth, distance, count, and existence
- Outperforms GPT-4o: On spatial understanding benchmarks while using only 7K training samples
Inference Template
Use the following template for inference:
You FIRST observe the image in <observe> </observe> tags, then visualise the relevant scene graph in <scene> </scene> tags, followed by thinking about the reasoning process as an internal monologue within <think> </think> tags and then provide the final answer. The final answer MUST BE put within <answer> </answer> tags, and only return the final choice including the correct option and answer within the answer tags, e.g., <answer> (A) cat </answer>.
Image size: {Width} x {Height}
Usage
from transformers import Qwen2_5_VLForConditionalGeneration, AutoProcessor
from PIL import Image
model = Qwen2_5_VLForConditionalGeneration.from_pretrained(
"OX-PIXL/SpatialThinker-3B",
torch_dtype="auto",
device_map="auto"
)
processor = AutoProcessor.from_pretrained("OX-PIXL/SpatialThinker-3B")
# Load image
image = Image.open("your_image.jpg")
width, height = image.size
# Prepare prompt with template
template = f"""You FIRST observe the image in <observe> </observe> tags, then visualise the relevant scene graph in <scene> </scene> tags, followed by thinking about the reasoning process as an internal monologue within <think> </think> tags and then provide the final answer. The final answer MUST BE put within <answer> </answer> tags, and only return the final choice including the correct option and answer within the answer tags, e.g., <answer> (A) cat </answer>.
Image size: {width} x {height}"""
question = "Where is the cat relative to the couch? (A) on top of (B) in front of (C) behind (D) beside"
messages = [
{
"role": "user",
"content": [
{"type": "image", "image": image},
{"type": "text", "text": template + "\n\n" + question},
],
}
]
text = processor.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
inputs = processor(text=[text], images=[image], return_tensors="pt").to(model.device)
generated_ids = model.generate(**inputs, max_new_tokens=1024)
output = processor.batch_decode(generated_ids, skip_special_tokens=True)[0]
print(output)
Citation
@misc{batra2025spatialthinkerreinforcing3dreasoning,
title={SpatialThinker: Reinforcing 3D Reasoning in Multimodal LLMs via Spatial Rewards},
author={Hunar Batra and Haoqin Tu and Hardy Chen and Yuanze Lin and Cihang Xie and Ronald Clark},
year={2025},
eprint={2511.07403},
archivePrefix={arXiv},
primaryClass={cs.CV},
url={https://arxiv.org/abs/2511.07403},
}
Links
- 📄 Paper: arXiv:2511.07403
- 🌐 Project Page: hunarbatra.com/SpatialThinker
- 💻 GitHub: github.com/hunarbatra/SpatialThinker
- 🤗 Dataset: OX-PIXL/STVQA-7K