USC, UCLA, and CMU Release Grid-Bench for Multi-Step Spatial Reasoning: 8,928 Executable Instances Reveal Severe State Drift Across 64-Step Trajectories
Can LLMs reliably maintain spatial state representations across sequential operations? USC, UCLA, and CMU introduced Grid-Bench (arXiv:2610.22312, GitHub: grid-bench/Grid-Bench), an executable benchmark with 8,928 instances testing 2D/3D/4D grid state transitions across history lengths up to T=64. Evaluations across 6 frontier models show steep degradation: while GPT-5.6 Sol and Claude 5 Sonnet retain strong cell accuracy, open-weight and mid-tier models collapse to near-zero exact world reconstruction over long trajectories.

Key Takeaways
- USC, UCLA, and CMU introduced Grid-Bench (arXiv:2610.22312), an executable spatial tracking benchmark across 2D, 3D, and 4D discrete manifolds
- Evaluates 8,928 instances across 8 spatial transformation rule families and trajectory lengths up to T=64 steps
- At intermediate length T=16, GPT-5.6 Sol (98.0% cell accuracy) and Claude 5 Sonnet (96.8%) lead while mid-tier models drop sharply
- At extreme length T=64, exact world recovery drops to 0 for GLM-5 and Kimi K2.5, demonstrating that long-horizon agents must rely on external state engines