Zhijie Xia

Streaming Reinforcement Learning2

  • Deep Policy Gradient Methods Without Batch Updates, Target Networks, or Replay Buffers

    Action Value Gradient enables deep policy-gradient reinforcement learning with fully incremental updates, without replay buffers, target networks, or batch updates.

    NeurIPS, 2024read
    streaming-rlincremental-learningpolicy-gradientactor-criticavgreinforcement-learning
  • Streaming Deep Reinforcement Learning Finally Works

    Stream-X introduces Stream TD, Stream Q, and Stream AC, enabling deep reinforcement learning directly from a stream of experience without replay buffers or batch updates.

    arXiv preprint, 2024read
    streaming-rlincremental-learningstream-xtemporal-difference-learningq-learningactor-critic

Piecewise Reinforcement Learning4

LLM Post-Training7

  • Learning to Foresee: Unveiling the Unlocking Efficiency of On-Policy Distillation

    This paper studies why on-policy distillation is more parameter-efficient than RL and argues that OPD develops foresight by identifying useful modules and stable low-rank update directions early in training.

    arXiv preprint, 2026read
    on-policy-distillationllm-post-trainingreinforcement-learninglow-rank-updatesoptimization
  • The Entropy Mechanism of Reinforcement Learning for Reasoning Language Models

    Why policy entropy collapses during RL for reasoning LLMs, how the entropy change reduces to a covariance between log-probability and logit change, and two covariance-based fixes, Clip-Cov and KL-Cov.

    arXiv, 2025read
    reinforcement-learningllm-reasoningpolicy-entropyentropy-collapsepolicy-gradientgrpoexploration
  • Does Reinforcement Learning Really Incentivize Reasoning Capacity in LLMs Beyond the Base Model?

    This paper uses large-k pass@k evaluation to argue that RLVR improves sampling efficiency without expanding the base model's reasoning boundary, while distillation from a stronger teacher does expand it.

    NeurIPS 2025, 2025read
    rlvrllm-post-trainingreinforcement-learningreasoningpass-at-kdistillation
  • The Reasoning Boundary Paradox: How Reinforcement Learning Constrains Language Models

    This paper traces RLVR's pass@k shrinkage to negative interference and on-policy winner-take-all dynamics, and proposes SELF, a greedy-failure filter plus forward KL that improves large-k coverage over GRPO.

    arXiv preprint, 2025read
    rlvrllm-post-trainingreinforcement-learningreasoningpass-at-klearning-dynamics
  • RL's Razor: Why Online Reinforcement Learning Forgets Less

    This paper shows RL forgets less than SFT at matched new-task accuracy, finds that KL from the base model on the new task predicts forgetting, and attributes RL's advantage to on-policy sampling.

    ICLR 2026, 2026read
    rlvrllm-post-trainingreinforcement-learningcatastrophic-forgettingkl-divergencecontinual-learning
  • The Unlearnability Phenomenon in RLVR for Language Models

    This paper shows that some hard training examples stay unlearnable under GRPO despite receiving correct rollouts, rules out optimization-side explanations, and attributes the failure to flawed representations that mid-training may fix.

    ICML 2026, 2026read
    rlvrllm-post-trainingreinforcement-learningreasoninglearning-dynamicsgradient-similarity

Continual Reinforcement Learning4

Policy Optimization1

  • Understanding the Impact of Entropy on Policy Optimization

    This paper argues entropy regularization helps policy gradient methods by smoothing the objective rather than only by encouraging exploration, using exact gradients in a gridworld and random-perturbation landscape probes in MuJoCo.

    ICML 2019, 2019read
    policy-gradiententropy-regularizationreinforcement-learningoptimization-landscapecurvaturehessian