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arXiv · 2605.25469

JacQuant: STE-Free Quantization-Aware Training via Learned Jacobian Surrogates

Kai Yi·Vignesh Vivekraja·Harshit Khaitan·Steven Li
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Abstract

Quantization-aware training (QAT) is widely deployed but typically relies on the Straight-Through Estimator (STE), which passes gradients through non-differentiable quantizers by fiat. This often makes training brittle near bin boundaries and weakly aligned with the actual behavior of the low-precision model. We introduce JacQuant, a QAT framework that learns a lightweight surrogate of the model's local sensitivity to parameter changes and uses it to stabilize and accelerate training within standard variance-reduced optimizers. The surrogate is inexpensive (diagonal or block-diagonal), data-driven, and compatible with common weight and activation quantizers. On code-preserving training phases, we prove convergence for non-convex objectives and obtain linear rates under a PL condition, and we relate the learned sensitivity to end-to-end output fidelity via a simple calibration argument. Across LLM benchmarks at $\leq 2$ bits, JacQuant consistently reaches higher accuracy than STE-based QAT, and the runtime analyses on various models show that the added cost remains negligible under practical group sizes. The method is drop-in and requires no changes to the forward quantizers; our empirical claims are scoped to ultra-low-bit LLM QAT.

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Kai Yi, Vignesh Vivekraja, Harshit Khaitan, Steven Li. 2026-05-25. JacQuant: STE-Free Quantization-Aware Training via Learned Jacobian Surrogates. https://arxiv.org/abs/2605.25469

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