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Hymba: A Hybrid-Head Architecture for Small Language Models (arxiv.org)
2 points by PaulHoule on Dec 11, 2024 | hide | past | pdf | discuss on HN

In plain words: Each layer mixes attention heads for exact recall with running-summary heads for cheap long memory, plus prepended tokens holding key facts. Its 1.5B version beats all models under 2 billion parameters and even a 3B rival, with 1.32% higher average accuracy and a much smaller cache.

Abstract · Hymba: A Hybrid-head Architecture for Small Language Models

We propose Hymba, a family of small language models featuring a hybrid-head parallel architecture that integrates transformer attention mechanisms with state space models (SSMs) for enhanced efficiency. Attention heads provide high-resolution recall, while SSM heads enable efficient context summarization. Additionally, we introduce learnable meta tokens that are prepended to prompts, storing critical information and alleviating the "forced-to-attend" burden associated with attention mechanisms. This model is further optimized by incorporating cross-layer key-value (KV) sharing and partial sliding window attention, resulting in a compact cache size. During development, we conducted a controlled study comparing various architectures under identical settings and observed significant advantages of our proposed architecture. Notably, Hymba achieves state-of-the-art results for small LMs: Our Hymba-1.5B-Base model surpasses all sub-2B public models in performance and even outperforms Llama-3.2-3B with 1.32% higher average accuracy, an 11.67x cache size reduction, and 3.49x throughput.

Xin Dong, Yonggan Fu, Shizhe Diao, Wonmin Byeon, Zijia Chen, Ameya Sunil Mahabaleshwarkar, Shih-Yang Liu, Matthijs Van Keirsbilck, Min-Hung Chen, Yoshi Suhara, Yingyan Lin, Jan Kautz, et al.
arXiv:2411.13676 · cs.CL, cs.AI, cs.LG · submitted Nov 20, 2024
abstract · pdf · html · 20 pages, models are available on huggingface

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