KVarN: Variance-Normalized KV-Cache Quantization Mitigates Error Accumulation in Reasoning Tasks

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Summary

KVarN is a calibration-free KV-cache quantizer that uses Hadamard rotation and dual-scaling variance normalization to reduce error accumulation during autoregressive decoding in large language models, achieving state-of-the-art 2-bit precision on reasoning benchmarks.

Test-time scaling is a powerful approach to obtain better reasoning in large language models, but it becomes memory-bottlenecked during long-horizon decoding, as the KV-cache grows. KV-cache quantization can help improve this, but current methods are evaluated under prefill-like settings and errors behave differently under autoregressive decoding. We show that in the latter regime, quantization errors accumulate across timesteps, driven primarily by incorrect token scales. We introduce KVarN, a calibration-free KV-cache quantizer that applies a Hadamard rotation followed by a dual-scaling variance normalization across both axes of the K and V matrices. We find that this combination fixes outlying token-scale errors and substantially reduces error accumulation over existing baselines. KVarN establishes a new state-of-theart for KV-cache quantization on generative benchmarks, including MATH500, AIME24 and HumanEval, at 2-bit precision. A vLLM implementation of the KVarN method is available at https://github.com/huawei-csl/KVarN
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Paper page - KVarN: Variance-Normalized KV-Cache Quantization Mitigates Error Accumulation in Reasoning Tasks

Source: https://huggingface.co/papers/2606.03458

Abstract

KVarN is a calibration-free KV-cache quantizer that uses Hadamard rotation and dual-scaling variance normalization to reduce error accumulation during autoregressive decoding in large language models.

Test-time scaling is a powerful approach to obtain better reasoning in large language models, but it becomes memory-bottlenecked during long-horizon decoding, as the KV-cache grows.KV-cache quantizationcan help improve this, but current methods are evaluated under prefill-like settings and errors behave differently underautoregressive decoding. We show that in the latter regime, quantization errors accumulate across timesteps, driven primarily by incorrecttoken scales. We introduceKVarN, a calibration-free KV-cache quantizer that applies aHadamard rotationfollowed by adual-scaling variance normalizationacross both axes of the K and V matrices. We find that this combination fixes outlying token-scale errors and substantially reduceserror accumulationover existing baselines.KVarNestablishes a new state-of-theart forKV-cache quantizationon generative benchmarks, including MATH500, AIME24 and HumanEval, at 2-bit precision. A vLLM implementation of theKVarNmethod is available at https://github.com/huawei-csl/KVarN

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