Fast Non-Episodic Finite-Horizon RL with K-Step Lookahead Thresholding
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Abstract (arXiv)
Online reinforcement learning in non-episodic, finite-horizon MDPs remains underexplored and is challenged by the need to estimate returns to a fixed terminal time. Existing infinite-horizon methods, which often rely on discounted contraction, do not naturally account for this fixed-horizon structure. We introduce a modified Q-function: rather than targeting the full-horizon, we learn a K-step lookahead Q-function that truncates planning to the next K steps. To further improve sample efficiency, we introduce a thresholding mechanism: actions are selected only when their estimated K-step lookahead value exceeds a time-varying threshold. We provide an efficient tabular learning algorithm for this novel objective, proving it achieves fast finite-sample convergence: it achieves minimax optimal constant regret for K=1 and O(max((K-1),CK-1)√SATlog(T)) regret for any K ≥ 2. We numerically evaluate the performance of our algorithm under the objective of maximizing reward. Our implementation adaptively increases K over time, balancing lookahead depth against estimation variance. Empirical results demonstrate superior cumulative rewards over state-of-the-art tabular RL methods across synthetic MDPs and RL environments: JumpRiverswim, FrozenLake and AnyTrading. Code is provided on hrefhttps://github.com/jamie01713/K-Step-Lookaheadgithub.
Key facts. No citing papers in the map yet (data through 7 Oct 2026). Builds on 29 of its 49 references that are in the map. First posted on arXiv 31 Jan 2026.
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