@inproceedings{kim-kang-2026-ta,
    title = "{TA}-{GRPO}-d: Trajectory-Aware {GRPO} for Optimizing Denoising Trajectories in Diffusion {LLM}s",
    author = "Kim, Gyunyeop  and
      Kang, Sangwoo",
    editor = "Liakata, Maria  and
      Moreira, Viviane P.  and
      Zhang, Jiajun  and
      Jurgens, David",
    booktitle = "Proceedings of the 64th Annual Meeting of the {A}ssociation for {C}omputational {L}inguistics (Volume 1: Long Papers)",
    month = jul,
    year = "2026",
    address = "San Diego, California, United States",
    publisher = "Association for Computational Linguistics",
    url = "https://preview.aclanthology.org/ingest-acl/2026.acl-long.1723/",
    pages = "37159--37174",
    ISBN = "979-8-89176-390-6",
    abstract = "Diffusion large language models (dLLMs) generate text by repeatedly unmasking a partially noised sequence in parallel, promising lower latency than autoregressive decoding. However, most discrete dLLMs still rely on fixed denoising schedules, which are non-adaptive to input difficulty and cannot learn efficient unmasking orders. This paper introduces a reinforcement learning (RL) framework that transforms dLLM decoding into a trajectory-aware, learnable policy. We propose a confidence-gated denoising strategy that dynamically decides which tokens to unmask and how many to unmask per step, enabling adaptive exploration of denoising trajectories. Building on Group Relative Policy Optimization, we reformulate it into a trajectory-aware variant, TA-GRPO-\textit{d}, which combines a trajectory-level signal{---}captured as the z-score of the AUC over intermediate rewards{---}with a token-level unmasking-time weight. This design allows the model to learn not only the final output quality but also the efficiency of the decoding path itself. Experiments on MATH-500, Countdown, Sudoku, and code benchmarks (HumanEval, MBPP) show that TA-GRPO-\textit{d} maintains or improves accuracy while reducing average denoising steps by up to half, achieving both faster inference and lower computational cost. Our approach provides an RL framework for optimizing dLLM decoding policies toward adaptive, efficient reasoning. Code is available at our GitHub."
}