Despite recent advances in Reinforcement learning with verifiable rewards (RLVR) for large language model (LLM) reasoning, most methods suffer from exploration collapse, as the semantic homogeneity of random rollouts traps models in narrow, over-optimized behaviors. Existing methods leverage policy entropy to encourage exploration, but face inherent limitations: global entropy regularization is susceptible to reward hacking, inducing meaningless verbosity, whereas local token-selective updates struggle with the strong inductive bias of pre-trained models. To this end, we propose Latent Policy Optimization via Iterative Information Bottleneck ( I²B-LPO), which shifts from statistical perturbation of token distributions to topological branching of reasoning trajectories. I²BLPO triggers latent branching at high-entropy states to diversify reasoning trajectories and applies the Information Bottleneck as a trajectory filter and self-reward to ensure concise and informative exploration. Empirical results on four mathematical benchmarks demonstrate that I²B-LPO achieves state-of-the-art performance, with margins of up to 5.3% in accuracy and 7.4% in diversity metrics. Code is available at https://github.com/denghuilin-cyber/IIB-LPO.

State-of-the-art vision-language models (VLMs) require massive scaling that limits practical deployment. Small-scale VLMs offer a practical alternative but face out-of-domain (OOD) collapse when trained with traditional supervised fine-tuning (SFT). Through GeneralPoints experiments, we identify that OOD collapse is due to SFT’s tendency to induce visual hallucinations under distribution shifts, whereas Reinforcement Learning’s (RL) bidirectional reward-driven mechanism with iterative error correction refines visual perception. Although RL-based post-training effectively mitigates OOD degradation, it faces a critical sparse reward dilemma in complex visual reasoning tasks. To this end, we propose Curriculum Reinforcement Finetuning (Curr-ReFT), comprising two sequential stages: (1) Structured Curriculum Reinforcement Learning, which progressively evolves task formats and reward functions to match models’ growing capabilities; and (2) Rejected Sampling-based Self-improvement, which maintains the fundamental capabilities of VLMs through selective learning from high-quality examples. Extensive experiments demonstrate that Curr-ReFT achieves state-of-the-art performance across various visual tasks in both in- and out-of-domain settings and benchmarks.