Preprint
Large Language Models

Molmo2: Open weights and data for vision-language models with video understanding and grounding

January 1, 2026

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2026

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Abstract

… Packing is non-trivial for vision-language models due to the need to efficiently pack both crops for the ViT and tokens for the LLM, and the need to support models with different …

Analysis

Why This Paper Matters

Molmo2 addresses a critical gap in the open-source AI ecosystem by providing open weights and data for vision-language models (VLMs) that excel in video understanding and grounding. While proprietary models like GPT-4V and Gemini have demonstrated impressive multimodal capabilities, their closed nature hinders reproducibility and broad accessibility. Molmo2's commitment to openness empowers researchers and practitioners to build upon state-of-the-art VLMs, fostering innovation and transparency.

The paper's focus on efficient packing of visual and textual tokens is particularly timely. As VLMs scale to handle high-resolution images and long videos, the computational cost of processing numerous crops and tokens becomes prohibitive. Molmo2's packing strategy likely optimizes training and inference, making it feasible to train large models on limited hardware. This efficiency is crucial for democratizing access to advanced multimodal AI.

Moreover, by explicitly targeting video understanding and grounding, Molmo2 pushes the boundaries of what open models can achieve. Video understanding is essential for applications like autonomous driving, surveillance, and content moderation, while grounding enables precise spatial reasoning. By releasing both weights and data, Molmo2 sets a new standard for open multimodal research.

Technical Contributions

  • Open Weights and Data: Molmo2 provides fully open model weights and training data, enabling reproducible research and fine-tuning for downstream tasks.
  • Efficient Packing for VLMs: The paper introduces a novel packing algorithm that efficiently handles both image crops for the vision transformer (ViT) and text tokens for the large language model (LLM), supporting models with diverse architectures.
  • Video Understanding and Grounding: The model is specifically designed to excel in video understanding and grounding tasks, extending beyond static image capabilities.
  • Scalability: The packing strategy likely reduces memory and compute requirements, making it feasible to train and deploy large VLMs on modest hardware.

Results

The abstract does not provide concrete metrics, but the release of open weights and data implies that Molmo2 achieves competitive performance on vision-language benchmarks, particularly those involving video and grounding. By enabling efficient packing, Molmo2 may demonstrate superior throughput and lower memory usage compared to baseline models. Future evaluations on standard datasets (e.g., MSRVTT, ActivityNet, RefCOCO) will likely show strong results, but these are not detailed in the abstract.

Significance

Molmo2's open-source approach has the potential to significantly impact the AI field by lowering barriers to entry for multimodal research. It enables academia and industry to build upon a strong foundation, accelerating progress in video understanding, grounding, and beyond. The efficient packing technique could become a standard for training large VLMs, promoting sustainability in AI research. Ultimately, Molmo2 contributes to a more inclusive and transparent AI ecosystem, where advanced capabilities are not confined to a few proprietary models.