REVIEW 4 major objections 7 minor 38 references
ZOQO: Zero-Order Quantized Optimization
T0 review · 4 major / 7 minor · reviewed 2026-08-10 · deepseek-v4-flash
Pith's one-line read ZOQO trains quantized models with forward-pass-only gradient signs and quantized updates, matching full-precision accuracy within a small margin.
desk verdict A genuine new ZO/quantized variant with a plausible LLM result, but the sign estimator on quantized losses is unverified and one table cell shows it can fail. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing mechanism is the sign of the loss difference between two symmetrical quantized perturbations, combined with a quantization-grid learning rate. Let s be the uniform quantization scale. Noise u is sampled from the discrete set B={−ms,…,0,…,ms} with m=max{⌊μ/s⌋,1}, and the gradient sign is estimated as sign(ℓ(x+u)−ℓ(x−u))·sign(u). The effective learning rate ηq=max{⌊η/s⌋,1}s ensures every parameter update is a multiple of s, so parameters never leave the quantized set. The loss values themselves are computed in floating point, but the paper notes that only their comparison is needed, not exact values.
What would settle it
Measure, on a small quantized network, the correlation between the ZOQO update direction sign(ℓ(x+u)−ℓ(x−u))·sign(u) and the true gradient sign over many random quantized weights; if the correlation is statistically indistinguishable from zero on the same tasks where ZOQO appears to work, the update is not estimating gradient sign and the performance would have to come from another mechanism.
Extended reading notes
Core claim
The central discovery is that replacing Gaussian noise with discrete quantized noise in a sign-based zero-order optimizer, and snapping the learning rate to multiples of the quantization scale, keeps the entire optimization trajectory on the quantized grid without collapsing performance. Concretely, the gradient sign is approximated as sign(ℓ(x+u)−ℓ(x−u))·sign(u), where u is drawn from the discrete set {−ms,…,ms}, and the update is x←x−ηq·sign(∇̂f) with ηq a multiple of the grid scale s. This requires no backward pass, no full-precision parameter storage, and no full-precision update arithmetic. In the reported experiments ZOQO attains an SST2 accuracy of 89.68% at 8 bits versus 91.06% for full-precision ZO-SignSGD with post-training quantization, and 64.34% at 4 bits, the best among the compared quantized variants; it also keeps black-box attack failure rates close to full-precision attacks, while cutting peak update memory from 903.71 MB to 371.21 MB on a toy model.
Load-bearing premise
The method assumes that comparing the losses at two neighboring quantized points tells you which direction lowers the loss, even though quantization makes the loss function piecewise constant and the comparison can be flat or noisy; the paper defers a proof of this to future work.
Editorial extensions
If this is right
- If ZOQO holds up, training a quantized model no longer requires a full-precision copy of weights or gradients, removing a major memory bottleneck in on-device learning.
- Black-box adversarial attacks can be launched in a fully quantized environment, meaning quantized deployments cannot assume safety from low-resource attackers.
- LoRA-style fine-tuning of LLMs can be performed with forward passes only and quantized updates, at 8-bit accuracy within about 1.5 points of full-precision fine-tuning.
- Lower bit budgets shift the advantage toward fully quantized training, where ZOQO outperforms partial-quantization baselines that leave the learning rate or noise in full precision.
- Memory savings scale with parameter dimension, since ZOQO stores 3bd bits for parameters and noise instead of an additional full-precision gradient of size b_FP d.
Reading between the lines
- Editorial inference: because only the sign of the loss difference is used, ZOQO could in principle be driven by any binary comparison oracle, such as human preference judgments, without needing exact loss values.
- Editorial inference: if the sign estimate remains informative in the nondifferentiable quantized landscape, the method should extend to other high-dimensional tasks such as reinforcement learning or distributed optimization, but this requires the deferred convergence theory to identify which loss landscapes satisfy that condition.
- Editorial inference: the uniform-quantization assumption is the main simplification; adaptive or per-layer quantization, which the paper itself mentions as future work, would likely reduce the accuracy gap at 4 bits.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces ZOQO, a zero-order quantized optimization method for training models with quantized parameters and updates. The algorithm adapts ZO-SignSGD by replacing Gaussian perturbations with noise sampled from a quantized grid B and by rounding the learning rate to a multiple of the quantization scale s, so that parameter updates remain on the quantized grid. The authors evaluate ZOQO in two settings: black-box adversarial attacks on MNIST, CIFAR-10, and ImageNet, and LoRA fine-tuning of OPT-1.3b on SST2, together with a toy-model memory simulation. The central claim is that ZOQO achieves competitive performance compared with full-precision methods while eliminating the need for full-precision first-order gradient and parameter-update calculations.
Significance. If the empirical claims hold, ZOQO offers a simple and potentially useful recipe for fully quantized, forward-only training in memory-constrained settings. The paper's strengths include the clean specification of Algorithm 1, the comparison against several quantization baselines, and the encouraging LLM fine-tuning results at 4-bit quantization in Table IV. The authors also acknowledge in Section V that convergence theory is deferred. However, the evidence is not yet conclusive: the key sign-estimation mechanism is unverified on discrete loss landscapes, no repeated trials or error bars are reported, and the memory benefit is only simulated on a toy model. These gaps are fixable and should be addressed before publication.
major comments (4)
- [Section III, Eq. (1) and Algorithm 1] The update direction is determined by sign(ℓ(x+u)-ℓ(x-u))·sign(u) with a single quantized perturbation u. Because quantization makes the loss piecewise constant and non-smooth, the ZO-SignSGD convergence guarantees from [1], which assume a smooth objective and Gaussian perturbations, do not apply; Section V explicitly defers convergence theory. The common scalar factor sign(ℓ(x+u)-ℓ(x-u)) multiplies every coordinate update, so a single erroneous comparison can flip all coordinate signs. Table I provides a concrete regime of concern: on naturally trained MNIST at b=4, RandSign+ZOQO attains a failure rate of 0.74 versus 0.32-0.33 for the FP and post-quantized baselines. The authors should either provide a convergence or bias analysis for the discrete perturbation model, or add direct measurements of sign fidelity (e.g., agreement with the sign of the true gradient or with multi-query estimates) across bit budgets.
- [Tables I-IV] None of the experimental tables report error bars, number of seeds, or per-run variance. The text gives evaluation set sizes but not how often the attack or fine-tuning procedure was repeated. Differences that are central to the claims, such as the MNIST b=4 natural RandSign failure rate 0.74 in Table I and the LLM b=4 ZOQO result in Table IV, cannot be distinguished from noise. Please report the mean and standard deviation (or at least multiple seeds) for each reported number and state the exact number of independent runs.
- [Section IV, Memory Efficiency; Section III memory formula] The memory claim is supported only by a simulation on a three-layer fully connected toy model (Table V) and by the formula M = 3bd + 2b_FP in Section III. The formula omits activations, optimizer states, loss/auxiliary tensors, and implementation-specific allocations, and the toy simulation is not the model used in any of the experiments. To support the memory advantage as a general claim, the authors should either measure peak memory on the actual MNIST/CIFAR-10/LLM experiments or clearly delimit the claim as an idealized parameter-storage analysis.
- [Section IV, LLM fine-tuning setup] The LoRA quantization range is set to twice the initial minimal and maximal parameter values, with no ablation or justification. Since s determines both the noise grid B (through m) and the quantized learning rate ηq (Eq. (3)), this range multiplier directly influences the algorithm's behavior and the reported LLM results. Please provide an ablation over this multiplier or a principled rule for setting it.
minor comments (7)
- [Section I] In the introduction, the method is called 'Zero-Order Quatized Optimization'; correct the spelling to 'Quantized'.
- [Algorithm 1, line 9] The update expression contains a stray closing brace: 'xi = clamp(...)(xi−1 − ηq · sign(∇f) });' — remove the extra brace.
- [Section III] The text says 'the discritization of the distribution'; 'discritization' should be 'discretization'.
- [Table II] The header '8-bit / 4-bit quantization' combined with slash-separated entries under 'Post quant.' and 'ZOQO' is ambiguous; label the subcolumns explicitly for each bit budget.
- [Table IV] The table mixes bit budgets in one row for ZOQO (b=(8/4)) while other methods have separate rows; reformat so each bit budget is a separate row or use explicit subcolumns.
- [Section III, memory formula] In the formula M = 3bd + 2b_FP, define the units of bd and state the value of b_FP used in the simulation; as written, 'bd' and 'bFP' are ambiguous.
- [Section III, notation] The convention for sign(ui) when ui = 0 is undefined; specify that sign(0) = 0 or exclude zero from the sampled noise.
Circularity Check
No significant circularity: ZOQO's design choices and empirical claims are self-contained, with no fitted parameter or self-citation chain that reduces a result to its inputs.
full rationale
The paper contains no derivation that equates a prediction with a fitted input. The method is defined by Algorithm 1, which combines the existing ZO-SignSGD update with quantized noise and a quantized learning rate. The noise distribution is constructed from the quantization grid B and the rescaled learning rate eta_q = max(floor(eta/s),1)s; these are design choices stated explicitly, not parameters fitted to the evaluation data. The central claims are supported by empirical comparisons on adversarial attacks and LLM fine-tuning, using external baselines and benchmarks: the attack experiments use the code of SignHunter [35] and the LLM experiments use the ZO benchmark [11] with the same hyperparameters. No self-citation by the authors is load-bearing: the cited ZO-SignSGD method is prior work by other authors, and its convergence theory is not invoked to prove ZOQO's performance; in fact, Section V explicitly defers convergence theory to future work. The absence of a proof that sign(loss(x+u)-loss(x-u)) is informative on a piecewise-constant quantized loss is a correctness risk, not circularity, because the assumption is an unverified premise rather than a result derived from itself. The factor-two range extension for LoRA initialization is a stated implementation choice, not a fitted constant renamed as a prediction. Overall, the paper's claims are validated by held-out empirical evaluation and are not circular.
Assumptions & free parameters
free parameters (1)
- LoRA quantization range multiplier =
2
assumptions (4)
- domain assumption The sign of the loss difference between two quantized perturbations remains informative for optimization when the loss is piecewise constant.
- domain assumption The initial quantization range [Rmin,Rmax] and scale s remain valid for the whole training run, and clamped parameters outside the range are not needed.
- domain assumption The discretized distribution D(B) over quantized noise levels approximates the Gaussian N(0,mu^2) well enough to preserve the zero-order sign estimate.
- domain assumption Loss values, despite being FP scalars, can be computed or approximated efficiently on edge devices, for example via hash tables.
Cite this review
Pith. "Pith review of ZOQO: Zero-Order Quantized Optimization." pith.science (2026). https://pith.science/paper/4QLMDNOA
@misc{pith2026250106736,
author = {Pith},
title = {Pith review of: ZOQO: Zero-Order Quantized Optimization},
year = {2026},
howpublished = {\url{https://pith.science/paper/4QLMDNOA}},
note = {Machine review of arXiv:2501.06736}
}
read the original abstract
The increasing computational and memory demands in deep learning present significant challenges, especially in resource-constrained environments. We introduce a zero-order quantized optimization (ZOQO) method designed for training models with quantized parameters and operations. Our approach leverages zero-order approximations of the gradient sign and adapts the learning process to maintain the parameters' quantization without the need for full-precision gradient calculations. We demonstrate the effectiveness of ZOQO through experiments in fine-tuning of large language models and black-box adversarial attacks. Despite the limitations of zero-order and quantized operations training, our method achieves competitive performance compared to full-precision methods, highlighting its potential for low-resource environments.
Figures
Reference graph
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