Hyperparameters are configuration variables controlling the behavior of machine learning algorithms. They are ubiquitous in machine learning and artificial intelligence and the choice of their values determines the effectiveness of systems based on these technologies. Manual hyperparameter search is often time-consuming and becomes infeasible when the number of hyperparameters is large. Automating the search is an important step towards advancing, streamlining, and systematizing machine learning, freeing researchers and practitioners alike from the burden of finding a good set of hyperparameters by trial and error. In this survey, we present a unified treatment of hyperparameter optimization, providing the reader with examples, insights into the state-of-the-art, and numerous links to further reading. We cover the main families of techniques to automate hyperparameter search, often referred to as hyperparameter optimization or tuning, including random and quasi-random search, bandit-, model-, population-, and gradient-based approaches. We further discuss extensions, including online, constrained, and multi-objective formulations, touch upon connections with other fields, such as meta-learning and neural architecture search, and conclude with open questions and future research directions.
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2 October 2025
Research Article|
October 02 2025
Hyperparameter optimization in machine learning Available to Purchase
Aaron Klein;
Aaron Klein
ScaDS.AI,
Leipzig University
, Germany
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Massimiliano Pontil;
Massimiliano Pontil
Istituto Italiano di Tecnologia
, Italy
, and University College London, UK
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Paolo Frasconi
Università di Firenze
, Italy
Corresponding author Paolo Frasconi paolo.frasconi@pm.me
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Corresponding author Paolo Frasconi paolo.frasconi@pm.me
Online ISSN: 1935-8245
Print ISSN: 1935-8237
© 2025 Luca Franceschi, Michele Donini, Valerio Perrone, Aaron Klein, Cédric Archambeau, Matthias Seeger, Massimiliano Pontil and Paolo Frasconi
2025
Luca Franceschi, Michele Donini, Valerio Perrone, Aaron Klein, Cédric Archambeau, Matthias Seeger, Massimiliano Pontil and Paolo Frasconi
Licensed re-use rights only
Foundations and Trends in Machine Learning (2025) 18 (6): 975–1109.
Citation
Franceschi L, Donini M, Perrone V, Klein A, Archambeau C, Seeger M, Pontil M, Frasconi P (2025), "Hyperparameter optimization in machine learning". Foundations and Trends in Machine Learning, Vol. 18 No. 6 pp. 975–1109, doi: https://doi.org/10.1561/2200000088
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