# SACQ: Structure-Aware Codebook Quantization for Ultra-Low-Bit Vision-Language-Action Models

**Authors:** Haesung Lee, Insu Han  
**Lab:** KAIST · **Published:** 30 Oct 2026  
**Links:** [arXiv](https://arxiv.org/abs/2610.41408) · [PDF](https://arxiv.org/pdf/2610.41408) · [This page](https://omen-bit.github.io/ai-paper-daily/paper/2610.41408.html)

## Key numbers

- **93.85%**: SACQ achieves 93.85% average success across four LIBERO suites at 1.5 bits per language/action weight while…
- **4.83×**: …across four LIBERO suites at 1.5 bits per language/action weight while reducing model memory by 4.83x.
- **93.55%**: it retains 93.55% success while running 1.51x faster than BF16

## Abstract

Vision-Language-Action (VLA) models enable capable robot behavior, but their large memory footprint limits deployment on resource-constrained robotic platforms. Weight quantization is a natural remedy, yet post-training quantization (PTQ) recipes inherited from large language models degrade when applied to VLAs at ultra-low precision. Existing low-bit PTQ methods often fail to explicitly account for the structure of downstream operations and allocate precision without considering its effect on the policy actions. We introduce SACQ, an ultra- low-bit weight-only vector-codebook quantization framework for VLAs. SACQ combines (1) structure-aware codebook fitting with role-specific quadratic metrics that reflect input statistics and downstream sensitivity; (2) action-aware mixed-bit allocation based on the increase in final-action error as individual layers are compressed; and (3) two-stage post-quantization refinement that reassigns codeword indices with second-order error compensation and calibrates codebooks and row-group scales against the decoded action. Using GR00T N1.7, SACQ achieves 93.85% average success across four LIBERO suites at 1.5 bits per language/action weight while reducing model memory by 4.83x. With INT8 activation quantization and low-precision attention, it retains 93.55% success while running 1.51x faster than BF16. On SimplER, SACQ further achieves 63.76% and 52.27% success under Visual Matching and Variant Aggregation at 2 bits per language/action weight, compared to 58.90% and 53.45% for BF16, respectively.

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