FastSLM: Hierarchical Temporal Abstraction for Efficient Long-Form Speech Adaptation

Junseok Lee; Chang-Jae Chun

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arXiv · 2601.06199

FastSLM: Hierarchical Temporal Abstraction for Efficient Long-Form Speech Adaptation

Junseok Lee·Chang-Jae Chun

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Abstract

Scaling Multimodal Large Language Models (MLLMs) to long-form speech is bottlenecked by the explosive growth of input tokens. Existing speech-language models project high-frame-rate acoustic features directly into the LLM input space, making long-context processing computationally prohibitive. Unlike images or videos, speech lacks spatial redundancy, making extreme token compression particularly challenging. To address this limitation, we propose FastSLM, a token-efficient architecture featuring the Hierarchical Temporal Abstractor (HTA), which progressively distills acoustic features across multiple temporal scales. HTA achieves an extreme compression rate of 1.67 tokens per second (97% reduction) while preserving essential linguistic information for downstream speech-language understanding. Experimental results demonstrate that FastSLM achieves competitive performance across diverse speech-language tasks while requiring substantially fewer speech tokens and FLOPs than existing speech-language models. The source code and model checkpoints are available at https://github.com/Lee-junseok1025/FastSLM.

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Junseok Lee, Chang-Jae Chun. 2026-08-31. FastSLM: Hierarchical Temporal Abstraction for Efficient Long-Form Speech Adaptation. https://arxiv.org/abs/2601.06199

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