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BitsMoE introduces a novel quantization framework for Mixture-of-Experts models by decomposing weights into shared and expert-specific spectral components to enable fine-grained bit allocation. By formulating precision assignment as an integer linear program based on activation-dependent costs, the method significantly improves memory efficiency and inference speed compared to existing approaches like GEMQ and GPTQ. This work advances the practical deployment of large-scale MoE architectures by addressing their inherent memory bottlenecks through structural heterogeneity exploitation.
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BitsMoE: Cost-Aware Bit Allocation in Spectral Space for MoE LLM Quantization

arXiv3 min read

arXiv:2606.00079v2 Announce Type: replace Abstract: Mixture-of-Experts (MoE) large language models incur substantial memory costs due to their large expert parameter counts. Mixed-precision quantization reduces these costs by allocating different bit-widths to experts or linear blocks according to their importance. However, assigning a single precision within each expert or linear block overlooks its internal structural heterogeneity. This limitation motivates two key questions: (1) how to define a fine-grained unit for quantization within a linear transformation; and (2) how to characterize the quantization cost of each unit under actual activation patterns and different bit-widths. To address these two questions, we propose BitsMoE, a cost-aware mixed-precision quantization framework built on two complementary techniques: (1) Shared-basis Spectral Decomposition (SSD) separates expert weights into a shared basis and expert-specific spectral components, defining structural quantization units while exploiting cross-expert redundancy. (2) Factorized Quantization Cost Modeling (FQCM) estimates component-wise costs from output reconstruction loss by combining intrinsic spectral importance, activation-dependent importance, and bit-width-dependent distortion. Using these component-wise costs, we formulate bit allocation as an integer linear program (ILP) that minimizes total modeled quantization cost under a fixed memory budget. On Qwen3-30B-A3B at 2-bit, BitsMoE achieves 64.29% average accuracy over seven downstream tasks, outperforming the evaluated MoE-specific methods, including those using ILP-based bit allocation, and exceeding GEMQ by 2.80 percentage points. Under the same setting, it achieves a $16.47\times$ end-to-end offline quantization speedup over GEMQ. It also achieves up to $6.46\times$ the decode throughput of GPTQ.

Abstract:Mixture-of-Experts (MoE) large language models incur substantial memory costs due to their large expert parameter counts. Mixed-precision quantization reduces these costs by allocating different bit-widths to experts or linear blocks according to their importance. However, assigning a single precision within each expert or linear block overlooks its internal structural heterogeneity. This limitation motivates two key questions: (1) how to define a fine-grained unit for quantization within a linear transformation; and (2) how to characterize the quantization cost of each unit under actual activation patterns and different bit-widths. To address these two questions, we propose BitsMoE, a cost-aware mixed-precision quantization framework built on two complementary techniques: (1) Shared-basis Spectral Decomposition (SSD) separates expert weights into a shared basis and expert-specific spectral components, defining structural quantization units while exploiting cross-expert redundancy. (2) Factorized Quantization Cost Modeling (FQCM) estimates component-wise costs from output reconstruction loss by combining intrinsic spectral importance, activation-dependent importance, and bit-width-dependent distortion. Using these component-wise costs, we formulate bit allocation as an integer linear program (ILP) that minimizes total modeled quantization cost under a fixed memory budget. On Qwen3-30B-A3B at 2-bit, BitsMoE achieves 64.29% average accuracy over seven downstream tasks, outperforming the evaluated MoE-specific methods, including those using ILP-based bit allocation, and exceeding GEMQ by 2.80 percentage points. Under the same setting, it achieves a $16.47\times$ end-to-end offline quantization speedup over GEMQ. It also achieves up to $6.46\times$ the decode throughput of GPTQ.

35 pages, 10 figures, 16 tables. Our code is available at this https URL and our models are available at this https URL

Machine Learning (cs.LG); Artificial Intelligence (cs.AI)

arXiv:2606.00079 [cs.LG]

(or arXiv:2606.00079v2 [cs.LG] for this version)

https://doi.org/10.48550/arXiv.2606.00079 Focus to learn more arXiv-issued DOI via DataCite

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Full text under the publisher's open licence · 351 words

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