FineWeb-Mask

📜 DATAMASK Paper | 💻 GitHub Repository | 📦 Fineweb-Mask Dataset

📚 Introduction

FineWeb-Mask is a 1.5 trillion token, high-efficiency pre-training dataset curated using the DATAMASK framework. Developed by the ByteDance Seed team, DATAMASK addresses the fundamental tension in large-scale data selection: the trade-off between high quality and high diversity.

By modeling data selection as a Mask Learning problem, we provide a derivative of the original FineWeb corpus. FineWeb-Mask is designed to eliminate semantic redundancy while preserving the highest quality samples, allowing models to achieve superior performance with significantly less data.

🎯 The Problem: The Quality-Diversity Trap

In large language model (LLM) pre-training, developers usually face two suboptimal choices:

1. The Quality Trap: Filtering solely by quality scores leads to "diminishing returns." Samples become highly clustered, resulting in severe semantic redundancy.
2. The Diversity Trap: Filtering solely for diversity often discards high-value quality samples, leading to worse performance than the original raw dataset.
3. The Compute Bottleneck: Traditional diversity algorithms (like greedy selection) are computationally prohibitive for trillion-token datasets.

💡 Highlights: The DATAMASK Framework

DATAMASK breaks this deadlock through a "joint harvesting" strategy:

• Joint Optimization: Uses Policy Gradient algorithms to optimize both quality and diversity metrics within a unified framework.
• Extreme Acceleration: Through probability relaxation and specialized optimization techniques, DATAMASK reduces computation time by 98.9% compared to traditional greedy algorithms, making trillion-token selection feasible.
• The "Balancer": Includes a tunable parameter that allows developers to define the "Golden Ratio" between quality and diversity for their specific needs.
• Semantic De-redundancy: Visual analysis shows that FineWeb-Mask samples are distributed evenly across high-quality regions rather than being rigidly clustered.

📈 Evaluation Results

FineWeb-Mask demonstrates that 1+1 > 2. By selecting a subset that represents only ~10% of the original scale in specific experiments, we observed:

• Dense Models: A 3.2% average improvement across 12 benchmarks for 1.5B dense models.
• MoE Models: A 1.9% improvement for 7B Mixture-of-Experts (MoE) models.
• Length Bias Correction: While quality filters favor long text and diversity filters favor short text, DATAMASK finds a scientific middle ground.

Model Size	Dataset	Avg. Score (12 Benchmarks)	Improvement
1.5B Dense	FineWeb (Original)	Baseline	-
1.5B Dense	FineWeb-Mask	+3.2%	🚀
7B MoE	FineWeb (Original)	Baseline	-
7B MoE	FineWeb-Mask	+1.9%	🚀

❤️ Acknowledgements

FineWeb-Mask is built upon the incredible foundational work of the HuggingFace FineWeb team. We are grateful to the open-source community for providing the raw corpora that made this optimization possible.

🌟 Citation

If you find our dataset or the DATAMASK framework useful, please cite our work:

@misc{fan2025jointselectionlargescalepretraining,
      title={Joint Selection for Large-Scale Pre-Training Data via Policy Gradient-based Mask Learning}, 
      author={Ziqing Fan and Yuqiao Xian and Yan Sun and Li Shen},
      year={2025},
      eprint={2512.24265},
      archivePrefix={arXiv},
      primaryClass={cs.CL},
      url={https://arxiv.org/abs/2512.24265}, 
}

💳 License

This dataset is released under the Apache 2.0 license. Users should also adhere to the original license terms of the FineWeb dataset and its constituent sources.

📧 Contact

• Ziqing Fan: [email protected]
• Yuqiao Xian: [email protected]

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Would you like me to help you draft the "How to Use" section for loading this dataset via the Hugging Face datasets library?