GPTQ: Accurate Post-Training Quantization for Generative Pre-trained Transformers

Authors: Elias Frantar, Saleh Ashkboos, Torsten Hoefler, Dan Alistarh

Submitted to arXiv on 31 Oct. 2022
License: CC BY 4.0
Abstract

Generative Pre-trained Transformer (GPT) models set themselves apart through breakthrough performance across complex language modelling tasks, but also by their extremely high computational and storage costs. Specifically, due to their massive size, even inference for large, highly-accurate GPT models may require multiple performant GPUs to execute, which limits the usability of such models. While there is emerging work on relieving this pressure via model compression, the applicability and performance of existing compression techniques is limited by the scale and complexity of GPT models. In this paper, we address this challenge, and propose GPTQ, a new one-shot weight quantization method based on approximate second-order information, that is both highly-accurate and highly-efficient. Specifically, GPTQ can quantize GPT models with 175 billion parameters in approximately four GPU hours, reducing the bitwidth down to 3 or 4 bits per weight, with negligible accuracy degradation relative to the uncompressed baseline. Our method more than doubles the compression gains relative to previously-proposed one-shot quantization methods, preserving accuracy, allowing us for the first time to execute an 175 billion-parameter model inside a single GPU. We show experimentally that these improvements can be leveraged for end-to-end inference speedups over FP16, of around 2x when using high-end GPUs (NVIDIA A100) and 4x when using more cost-effective ones (NVIDIA A6000). The implementation is available at https://github.com/IST-DASLab/gptq.

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    GPTQT: Quantize Large Language Models Twice to Push the Efficiency
    Yi-Pin Guo, Yi-Lin Lang, Qinyuan Ren · 2024 · 2024 IEEE International Conference on Cybernetics and Intelligent Systems (CIS) and IEEE International Conference on Rob · cited 5 times · Not summarized yet
    Abstract

    Due to their large size, generative Large Language Models (LLMs) require significant computing and storage resources. This paper introduces a new post-training quantization method, GPTQT, to reduce memory usage and enhance processing speed by expressing the weight of LLM in 3bit/2bit. Practice has shown that minimizing the quantization error of weights is ineffective, leading to overfitting. Therefore, GPTQT employs a progressive two-step approach: initially quantizing weights using Linear quantization to a relatively high bit, followed by converting obtained int weight to lower bit binary coding. A re-explore strategy is proposed to optimize initial scaling factor. During inference, these s…

  2. Very close Cites this paper
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    Eli S. Levy, Adam Teman, Yoni Pugachov · 2026 · Not summarized yet
    Abstract

    Post-training quantization (PTQ) enables efficient deployment, yet transformer architectures remain challenging to quantize due to nonlinear layers. While existing methods attribute accuracy loss to insufficient numerical precision, often necessitating floating-point fallbacks, we demonstrate that degradation is actually driven by specific structural error sources. We find that learned scale parameters in normalization layers and compounded approximations in GELU are the primary error contributors, whereas SoftMax remains inherently robust to aggressive quantization. To address these bottlenecks, we introduce TR-PTQ, a unified integer-only formulation using shared Taylor Region (TR) exponent…

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    Junhan Kim, Chungman Lee, Eulrang Cho et al. · 2024 · Neural Information Processing Systems · cited 11 times · Not summarized yet
    Abstract

    With the increasing complexity of generative AI models, post-training quantization (PTQ) has emerged as a promising solution for deploying hyper-scale models on edge devices such as mobile and TVs. Existing PTQ schemes, however, consume considerable time and resources, which could be a bottleneck in real situations where frequent model updates and multiple hyperparameter tunings are required. As a cost-effective alternative, learning-free PTQ schemes have been proposed. However, the performance is somewhat limited because they cannot consider the inter-layer dependency within the attention module, which is a significant feature of Transformers. In this paper, we thus propose a novel PTQ algo…

  4. Very close Cited by this paper Used in depth by this paper A method it uses
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    Z. Yao, Reza Yazdani Aminabadi, Minjia Zhang et al. · 2022 · Neural Information Processing Systems · cited 840 times · Not summarized yet
    Abstract

    How to efficiently serve ever-larger trained natural language models in practice has become exceptionally challenging even for powerful cloud servers due to their prohibitive memory/computation requirements. In this work, we present an efficient and affordable post-training quantization approach to compress large Transformer-based models, termed as ZeroQuant. ZeroQuant is an end-to-end quantization and inference pipeline with three main components: (1) a fine-grained hardware-friendly quantization scheme for both weight and activations; (2) a novel affordable layer-by-layer knowledge distillation algorithm (LKD) even without the access to the original training data; (3) a highly-optimized qu…

  5. Very close Cites this paper
    MPQ: A Message-Passing View of Post-Training Quantization
    Yan-Shuo Chen, Chen-Xi Liu, Reza Shirkavand et al. · 2026 · Not summarized yet
    Abstract

    Post-training quantization (PTQ) is a key technique for efficiently deploying large language models, as it compresses weights into low-bit representations without retraining. Existing PTQ solvers, including GPTQ, LDLQ, and block coordinate descent, commit each weight block to a single codeword before its neighbors are considered, leaving near-optimal alternatives unexplored. In this work, we cast row-wise PTQ as posterior inference over discrete codebooks, in which existing solvers correspond to a zero-temperature, hard-decision limit retaining only the top codeword per block. We propose Message-Passing Quantization (MPQ), which preserves soft posterior information across blocks during infer…

  6. Very close
    SEPTQ: A Simple and Effective Post-Training Quantization Paradigm for Large Language Models
    Han Liu, Haotian Gao, Xiao-Tong Zhang et al. · 2025 · Knowledge Discovery and Data Mining · cited 7 times · Not summarized yet
    Abstract

    Large language models (LLMs) have shown remarkable performance in various domains, but they are constrained by massive computational and storage costs. Quantization, an effective technique for compressing models to fit resource-limited devices while preserving generative quality, encompasses two primary methods: quantization aware training (QAT) and post-training quantization (PTQ). QAT involves additional retraining or fine-tuning, thus inevitably resulting in high training cost and making it unsuitable for LLMs. Consequently, PTQ has become the research hotspot in recent quantization methods. However, existing PTQ methods usually rely on various complex computation procedures and suffer fr…

  7. Very close Another approach to the problem
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    GPTVQ proposes Hessian-guided post-training vector quantization for large language models, addressing the same model-compression problem with a different quantization method.

    Abstract

    In this work we show that the size versus accuracy trade-off of neural network quantization can be significantly improved by increasing the quantization dimensionality. We propose the GPTVQ method, a new fast method for post-training vector quantization (VQ) that scales well to Large Language Models (LLMs). Our method interleaves quantization of one or more columns with updates to the remaining unquantized weights, using information from the Hessian of the per-layer output reconstruction MSE. Quantization codebooks are initialized using an efficient data-aware version of the EM algorithm. The codebooks are then updated, and further compressed by using integer quantization and SVD-based compr…

  8. Very close
    Compression of Generative Pre-trained Language Models via Quantization
    Chaofan Tao, Lu Hou, Wei Zhang et al. · 2022 · Annual Meeting of the Association for Computational Linguistics · cited 120 times · Not summarized yet
    Abstract

    The increasing size of generative Pre-trained Language Models (PLMs) have greatly increased the demand for model compression. Despite various methods to compress BERT or its variants, there are few attempts to compress generative PLMs, and the underlying difficulty remains unclear. In this paper, we compress generative PLMs by quantization. We find that previous quantization methods fail on generative tasks due to the homogeneous word embeddings caused by reduced capacity and the varied distribution of weights. Correspondingly, we propose a token-level contrastive distillation to learn distinguishable word embeddings, and a module-wise dynamic scaling to make quantizers adaptive to different…

Prior work it builds on

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    Abstract

    We consider the problem of model compression for deep neural networks (DNNs) in the challenging one-shot/post-training setting, in which we are given an accurate trained model, and must compress it without any retraining, based only on a small amount of calibration input data. This problem has become popular in view of the emerging software and hardware support for executing models compressed via pruning and/or quantization with speedup, and well-performing solutions have been proposed independently for both compression approaches. In this paper, we introduce a new compression framework which covers both weight pruning and quantization in a unified setting, is time- and space-efficient, and …

  2. Close Used in depth by this paper A method it uses
    BRECQ: Pushing the Limit of Post-Training Quantization by Block Reconstruction
    Yuhang Li, Ruihao Gong, Xu Tan et al. · 2021 · International Conference on Learning Representations · cited 772 times · Not summarized yet
    Abstract

    We study the challenging task of neural network quantization without end-to-end retraining, called Post-training Quantization (PTQ). PTQ usually requires a small subset of training data but produces less powerful quantized models than Quantization-Aware Training (QAT). In this work, we propose a novel PTQ framework, dubbed BRECQ, which pushes the limits of bitwidth in PTQ down to INT2 for the first time. BRECQ leverages the basic building blocks in neural networks and reconstructs them one-by-one. In a comprehensive theoretical study of the second-order error, we show that BRECQ achieves a good balance between cross-layer dependency and generalization error. To further employ the power of qu…

  3. Close Same question Used in depth by this paper
    LLM.int8(): 8-bit Matrix Multiplication for Transformers at Scale
    Tim Dettmers, Mike Lewis, Younes Belkada et al. · 2022 · Machine Learning · cited 1,403 times · AI summary available

    LLM.int8() reduces inference memory for large transformer language models through 8-bit matrix multiplication while retaining performance.

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    Large language models have been widely adopted but require significant GPU memory for inference. We develop a procedure for Int8 matrix multiplication for feed-forward and attention projection layers in transformers, which cut the memory needed for inference by half while retaining full precision performance. With our method, a 175B parameter 16/32-bit checkpoint can be loaded, converted to Int8, and used immediately without performance degradation. This is made possible by understanding and working around properties of highly systematic emergent features in transformer language models that dominate attention and transformer predictive performance. To cope with these features, we develop a t…

  4. Close Used in depth by this paper A method it uses
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Papers that cite it

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