arXiv:2608.12959cs.LGcs.AI2026-08

模型预测能力够强,但规划目标缺陷导致长程规划失败。

The Objective Is the Bottleneck: Latent World Models Encode What Their Planners Cannot Use

  • 用交叉熵方法优化规划目标,而非仅追求预测准确
  • 替换目标后长程规划成功率从26%升至98%,且更省计算资源
  • 模型已掌握环境信息,失败源于规划机制设计问题

在复现LeWorldModel于TwoRoom任务中发现,长时程规划失败的根源并非预测器性能不足,而是规划目标设计缺陷。尽管模型能准确预测75步后的状态(误差仅0.189,相当于世界冻结时的误差),但规划器仅能有效想象前25步。基于交叉熵的规划最小化平方潜在距离,该指标在真实距离相关性为0.426,80单位后饱和,超过120单位反而下降,导致远离目标反而降低代价。信息始终存在:通过脊线探测器可从冻结嵌入中恢复位置,决定系数高达0.9922。该问题存在于原始作者权重中,并在四个检查点上表现出长程成功度与度量质量正相关、与预测准确率负相关。仅更换目标函数,无需重训练或使用GPU,即可将100步偏移处的目标达成率从26.0%提升至98.0%,达到25步水平,且消耗资源仅为三分之一。学习帧间分离的头虽空间预测相关性较低(r=0.819),但因捕捉可达性而非距离,规划表现更优,过墙成本高出24%,而平方潜在距离仅高4%。

原文摘要 · Abstract (English)

Latent world models are judged by how well they predict, so when planning fails at long horizons the natural reading is that the predictor degrades. On a reproduction of LeWorldModel on TwoRoom we show the binding constraint is the planner's objective instead. The predictor is not the limit: its imagined state seventy-five environment steps ahead is still only 0.189 as wrong as assuming the world froze, while the planner never imagines beyond twenty-five. The objective is. Cross-entropy-method planning minimises squared latent distance, which tracks true distance at r = 0.426, saturates by about eighty arena units and decreases beyond a hundred and twenty, so moving away from the goal can lower the cost. The information is present throughout: a ridge probe recovers position from the frozen embedding at R^2 0.9922. The pathology is the method's, not one reimplementation's. It is present in the authors' released weights, and across four checkpoints long-horizon success rank-orders exactly with metric quality and inversely with prediction accuracy. Replacing only the objective, with nothing retrained and no GPU, lifts goals reached at offset 100 from 26.0% to 98.0%, equals the 98.0% at offset 25, and reaches 92.0% under a third of the budget: planning stops depending on the horizon. The best cost is not the most accurate. A head learned from frame separation alone predicts spatial distance worse than a position probe (r = 0.819 against 0.9897) yet plans better, charging 24% more to cross the environment's dividing wall where squared latent distance charges 4% less. It has learned reachability, not proximity.

世界模型规划算法目标设计长程推理

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