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Reward hacking -- where RL agents exploit gaps in misspecified reward functions -- has been widely observed, but not yet systematically studied. To understand how reward hacking arises, we construct four RL environments with misspecified…

Machine Learning · Computer Science 2022-02-15 Alexander Pan , Kush Bhatia , Jacob Steinhardt

Sparse and delayed rewards pose a challenge to single agent reinforcement learning. This challenge is amplified in multi-agent reinforcement learning (MARL) where credit assignment of these rewards needs to happen not only across time, but…

Machine Learning · Computer Science 2022-11-01 Jennifer She , Jayesh K. Gupta , Mykel J. Kochenderfer

Offline reinforcement learning (RL) enables policy learning from pre-collected datasets, avoiding costly and risky online interactions, but it often struggles with long-horizon tasks involving sparse rewards. Existing goal-conditioned and…

Machine Learning · Computer Science 2026-01-14 Chengyang Gu , Yuxin Pan , Hui Xiong , Yize Chen

Auxiliary Learning (AL) is a form of multi-task learning in which a model trains on auxiliary tasks to boost performance on a primary objective. While AL has improved generalization across domains such as navigation, image classification,…

Machine Learning · Computer Science 2025-11-05 Judah Goldfeder , Matthew So , Hod Lipson

Efficient exploration in multi-agent reinforcement learning (MARL) is a challenging problem when receiving only a team reward, especially in environments with sparse rewards. A powerful method to mitigate this issue involves crafting dense…

Machine Learning · Computer Science 2025-07-28 Xuefei Wu , Xiao Yin , Yuanyang Zhu , Chunlin Chen

Reward models are pivotal for aligning Large Language Models (LLMs) with human preferences. Existing approaches face two key limitations: Discriminative reward models require large-scale annotated data, as they cannot exploit the preference…

Computation and Language · Computer Science 2026-02-03 Yongfu Xue

The aim of Inverse Reinforcement Learning (IRL) is to infer a reward function $R$ from a policy $\pi$. This problem is difficult, for several reasons. First of all, there are typically multiple reward functions which are compatible with a…

Machine Learning · Computer Science 2024-11-26 Joar Skalse , Alessandro Abate

Large language models (LLMs) are probabilistic in nature and perform more reliably when augmented with external information. As complex queries often require multi-step reasoning over the retrieved information, with no clear or…

Information Retrieval · Computer Science 2026-04-10 Roxana Petcu , Evangelos Kanoulas , Maarten de Rijke

Conventional video summarization approaches based on reinforcement learning have the problem that the reward can only be received after the whole summary is generated. Such kind of reward is sparse and it makes reinforcement learning hard…

Computer Vision and Pattern Recognition · Computer Science 2020-03-03 Yiyan Chen , Li Tao , Xueting Wang , Toshihiko Yamasaki

Sparse-reward reinforcement learning (RL) can model a wide range of highly complex tasks. Solving sparse-reward tasks is RL's core premise, requiring efficient exploration coupled with long-horizon credit assignment, and overcoming these…

Machine Learning · Computer Science 2025-10-21 Leander Diaz-Bone , Marco Bagatella , Jonas Hübotter , Andreas Krause

Episodic tasks in Reinforcement Learning (RL) often pose challenges due to sparse reward signals and high-dimensional state spaces, which hinder efficient learning. Additionally, these tasks often feature hidden "trap states" --…

Machine Learning · Computer Science 2025-05-23 Yuxuan Li , Yicheng Gao , Ning Yang , Stephen Xia

Recent work has shown that deep reinforcement-learning agents can learn to follow language-like instructions from infrequent environment rewards. However, this places on environment designers the onus of designing language-conditional…

Artificial Intelligence · Computer Science 2019-12-24 Dzmitry Bahdanau , Felix Hill , Jan Leike , Edward Hughes , Arian Hosseini , Pushmeet Kohli , Edward Grefenstette

Reinforcement learning usually uses the feedback rewards of environmental to train agents. But the rewards in the actual environment are sparse, and even some environments will not rewards. Most of the current methods are difficult to get…

Machine Learning · Computer Science 2020-01-13 Kai Jiang , XiaoLong Qin

Deep reinforcement learning algorithms require large amounts of experience to learn an individual task. While in principle meta-reinforcement learning (meta-RL) algorithms enable agents to learn new skills from small amounts of experience,…

Machine Learning · Computer Science 2019-03-21 Kate Rakelly , Aurick Zhou , Deirdre Quillen , Chelsea Finn , Sergey Levine

Reinforcement learning (RL) has demonstrated compelling performance in robotic tasks, but its success often hinges on the design of complex, ad hoc reward functions. Researchers have explored how Large Language Models (LLMs) could enable…

Robotics · Computer Science 2025-05-13 Letian Chen , Nina Moorman , Matthew Gombolay

Reinforcement learning (RL) often struggles to accomplish a sparse-reward long-horizon task in a complex environment. Goal-conditioned reinforcement learning (GCRL) has been employed to tackle this difficult problem via a curriculum of…

Machine Learning · Computer Science 2023-12-20 Lisheng Wu , Ke Chen

Many continuous control problems can be formulated as sparse-reward reinforcement learning (RL) tasks. In principle, online RL methods can automatically explore the state space to solve each new task. However, discovering sequences of…

Mastering deep reinforcement learning (DRL) proves challenging in tasks featuring scant rewards. These limited rewards merely signify whether the task is partially or entirely accomplished, necessitating various exploration actions before…

Machine Learning · Computer Science 2024-04-11 Guojian Wang , Faguo Wu , Xiao Zhang

This paper presents a novel form of policy gradient for model-free reinforcement learning (RL) with improved exploration properties. Current policy-based methods use entropy regularization to encourage undirected exploration of the reward…

Machine Learning · Computer Science 2017-03-17 Ofir Nachum , Mohammad Norouzi , Dale Schuurmans

Reinforcement learning (RL) has enabled the training of large language model (LLM) agents to interact with the environment and to solve multi-turn long-horizon tasks. However, the RL-trained agents often struggle in tasks that require…

Machine Learning · Computer Science 2026-03-10 Yulun Jiang , Liangze Jiang , Damien Teney , Michael Moor , Maria Brbic