InfoQuant: Shaping Activation Distributions for Low-Bit LLM Quantization

• URL: http://arxiv.org/abs/2605.26175v1
• Date: Mon, 25 May 2026 05:34:46 GMT
• Title: InfoQuant: Shaping Activation Distributions for Low-Bit LLM Quantization
• Abstract summary: Low-bit activation quantization remains a major bottleneck in large language model (LLM) deployment.<n>Existing post-training quantization methods suppress peaks, balance channels, or minimize reconstruction error.<n>We recast activation transformation as quantizer-facing distribution design and analyze quantization error from an information-theoretic perspective.<n>We propose InfoQuant, a train-free method that employs Peak Suppression Orthogonal Transformation (PSOT) to shape activations into more quantization-friendly distributions.
• Score: 16.236156118201116
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Low-bit activation quantization remains a major bottleneck in efficient large language model (LLM) deployment. The difficulty is not only that activations contain outliers, but that their distributions are often poorly matched to a low-bit uniform quantizer. Existing post-training quantization (PTQ) methods suppress peaks, balance channels, or minimize reconstruction error, yet they rarely specify what activation distribution is actually easy to discretize. As a result, activations may appear numerically smoother while still incurring large quantization error because the quantization range remains wide or most values collapse into a few levels near the mean. We recast activation transformation as quantizer-facing distribution design and analyze quantization error from an information-theoretic perspective. Our analysis shows that quantization-friendly activations should jointly have a smaller numerical range and sufficient dispersion within that range. Guided by this analysis, we propose InfoQuant, a train-free method that employs Peak Suppression Orthogonal Transformation (PSOT) to shape activations into more quantization-friendly distributions. We further introduce adaptive outlier-token selection to improve the robustness of PSOT during optimization. Across multiple LLM families, InfoQuant consistently outperforms prior PTQ and end-to-end training baselines. Under W4A4KV4, it preserves 97% of floating-point accuracy on average and reduces the LLaMA-2 13B performance gap by 42% over the previous state of the art. Code is available at [https://github.com/LLIKKE/InfoQuant](https://github.com/LLIKKE/InfoQuant)

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