OX-PIXL/SpatialThinker-3B

VISIONPricing:Input $0.32 / Cached $0.016 / Output $1.6Concurrent Unit Cost:1Model Size:3BQuant:BF16Context Size:32kPublished:Nov 7, 2025License:apache-2.0Architecture:Transformer0.0K Open Weights Featherless Exclusive Cold

SpatialThinker-3B by OX-PIXL is a 3 billion parameter 3D-aware multimodal large language model (MLLM) built on Qwen2.5-VL-3B-Instruct. It integrates structured spatial grounding with multi-step reasoning, simulating human-like spatial perception by constructing scene graphs and using dense spatial rewards during training. This model excels at complex spatial understanding tasks across nine categories, outperforming larger models like GPT-4o on specific spatial benchmarks.

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SpatialThinker-3B Overview

SpatialThinker-3B is a 3D-aware multimodal large language model (MLLM) developed by researchers from the University of Oxford and UC Santa Cruz. Built upon the Qwen2.5-VL-3B-Instruct base model, it features a 3 billion parameter architecture and a 32K context length. This model is uniquely trained with Group Relative Policy Optimization (GRPO) and dense spatial rewards, enabling it to simulate human-like spatial perception and reasoning.

Key Capabilities

  • Structured Spatial Reasoning: Constructs detailed, question-focused scene subgraphs, including objects, bounding boxes, and their spatial relations.
  • Advanced Reward System: Utilizes a multi-objective reward function during training that enforces correct format, count, accuracy, and crucial spatial grounding.
  • Comprehensive Spatial Understanding: Proficient across nine distinct spatial reasoning categories: relations, reach, size, orientation, instance location, depth, distance, count, and existence.
  • High Performance: Demonstrates superior performance on spatial understanding benchmarks, even outperforming models like GPT-4o, despite being trained on a relatively small dataset of 7,587 spatial VQA samples (STVQA-7K).

Good for

  • Applications requiring precise 3D spatial understanding and reasoning from images.
  • Tasks involving complex object relationships and positional queries.
  • Research and development in multimodal AI focusing on spatial intelligence.
  • Scenarios where a smaller, efficient model can achieve high accuracy on specialized spatial tasks.