DP-LAC: Lightweight Adaptive Clipping for Differentially Private Federated Fine-tuning of Language Models

Fuente: arXiv
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Autores principales: Mehmood, Haaris, Xu, Jie, Saravanan, Karthikeyan, Van Dalen, Rogier, Ozay, Mete
Formato: Preprint
Publicado: 2026
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author Mehmood, Haaris
Xu, Jie
Saravanan, Karthikeyan
Van Dalen, Rogier
Ozay, Mete
author_facet Mehmood, Haaris
Xu, Jie
Saravanan, Karthikeyan
Van Dalen, Rogier
Ozay, Mete
contents Federated learning (FL) enables the collaborative training of large-scale language models (LLMs) across edge devices while keeping user data on-device. However, FL still exposes sensitive information through client-provided gradients. Differentially private stochastic gradient descent (DP-SGD) mitigates this risk by clipping each client's contribution to a threshold $C$ and adding noise proportional to $C$. Existing adaptive clipping techniques dynamically adjust $C$ but demand tedious hyperparameter tuning, which can erode the privacy budget. In this paper, we introduce DP-LAC, a method that first estimates an initial clipping threshold within an order of magnitude of the optimum using private histogram estimation, and then adapts this threshold during training without consuming additional privacy budget or introducing new hyperparameters. Empirical results show that DP-LAC outperforms both state-of-the-art adaptive clipping methods and vanilla DP-SGD, achieving an average accuracy gain of $6.6\%$.
format Preprint
id arxiv_https___arxiv_org_abs_2605_10272
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle DP-LAC: Lightweight Adaptive Clipping for Differentially Private Federated Fine-tuning of Language Models
Mehmood, Haaris
Xu, Jie
Saravanan, Karthikeyan
Van Dalen, Rogier
Ozay, Mete
Machine Learning
Artificial Intelligence
Cryptography and Security
Distributed, Parallel, and Cluster Computing
Federated learning (FL) enables the collaborative training of large-scale language models (LLMs) across edge devices while keeping user data on-device. However, FL still exposes sensitive information through client-provided gradients. Differentially private stochastic gradient descent (DP-SGD) mitigates this risk by clipping each client's contribution to a threshold $C$ and adding noise proportional to $C$. Existing adaptive clipping techniques dynamically adjust $C$ but demand tedious hyperparameter tuning, which can erode the privacy budget. In this paper, we introduce DP-LAC, a method that first estimates an initial clipping threshold within an order of magnitude of the optimum using private histogram estimation, and then adapts this threshold during training without consuming additional privacy budget or introducing new hyperparameters. Empirical results show that DP-LAC outperforms both state-of-the-art adaptive clipping methods and vanilla DP-SGD, achieving an average accuracy gain of $6.6\%$.
title DP-LAC: Lightweight Adaptive Clipping for Differentially Private Federated Fine-tuning of Language Models
topic Machine Learning
Artificial Intelligence
Cryptography and Security
Distributed, Parallel, and Cluster Computing
url https://arxiv.org/abs/2605.10272