arXiv — Machine Learning · · 3 min read

EVA-0: Test-Time Model Evolution with Only Two Forward Passes per Sample

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Computer Science > Machine Learning

arXiv:2605.18867 (cs)
[Submitted on 15 May 2026]

Title:EVA-0: Test-Time Model Evolution with Only Two Forward Passes per Sample

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Abstract:Test-time model evolution offers a promising way for deployed models to improve from unlabeled test-time experience, yet most existing methods depend on backpropagation (BP), which incurs substantial memory overhead and makes them difficult to deploy on edge devices, quantized models, specialized accelerators, or black-box models. In this work, we study test-time model evolution under a strict two-forward budget, a setting that pushes adaptation toward highly efficient real-world deployment. We reveal three key obstacles in zeroth-order test-time optimization: susceptibility to shortcut solutions, uncontrolled weight drift, and ineffective update direction estimation. To overcome them, we propose EVA-0, a minimal zeroth-order adaptation framework that: 1) keeps the loss scale-invariant to prevent shortcut solutions; 2) devises an anchor-guided optimization strategy to alleviate weight drift; 3) uses sample-wise symmetric two-sided perturbation for update direction estimation and inference. EVA-0 requires no BP and performs both inference and adaptation within only two forward passes per sample. Results on ImageNet-C & ViT-Base show that EVA-0 outperforms both BP-based DeYO and BP-free FOA, while achieving a 14x speed-up over FOA. Code will be released.
Subjects: Machine Learning (cs.LG); Artificial Intelligence (cs.AI)
Cite as: arXiv:2605.18867 [cs.LG]
  (or arXiv:2605.18867v1 [cs.LG] for this version)
  https://doi.org/10.48550/arXiv.2605.18867
arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Guohao Chen [view email]
[v1] Fri, 15 May 2026 09:26:02 UTC (538 KB)
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