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When Planning Problems Become Hard for LLMs: Separating Structural Complexity from Semantic Interpretability

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Based on a feed excerpt; full article content has not been acquired. Source evidence retrieved 21/10/2026, 04:03:25 UTC.

Briefings

A new study by researchers at arXiv:2610.26964 investigates whether LLMs struggle with planning due to structural complexity or semantic interpretation. Using seven STRIPS domains, the researchers found that a zero-training delete-relaxation heuristic ($h_{\mathrm{add}}$) significantly outperforms learned alternatives for predicting structural difficulty, achieving a mean Spearman correlation of 0.931. The study also found that LLMs fail to plan effectively when semantic predicates are renamed, dropping success from 67.5% to 40.0%, while refusals remain at 0%. The authors conclude that established symbolic heuristics already estimate structural difficulty well, suggesting future improvements require modeling LLM behavior sensitive to predicate semantics rather than developing more structural predictors.

Key points

• A zero-training delete-relaxation heuristic ($h_{\mathrm{add}}$) outperforms learned alternatives for predicting structural difficulty in LLMs, achieving a mean Spearman correlation of 0.931 across seven STRIPS domains.
• LLMs fail to plan effectively when semantic predicates are renamed, dropping success from 67.5% to 40.0% while refusals remain at 0%.

Context

This research addresses a gap in understanding LLM planning limitations by distinguishing between structural complexity and semantic interpretation. The study uses seven STRIPS domains with BFS-optimal plan lengths to isolate these factors, revealing that symbolic heuristics already capture structural difficulty well.

Limitations

The evidence is limited to seven STRIPS domains with BFS-optimal plan lengths. The study does not provide causal claims or opinions, and the findings are based on held-out domains rather than solving specific instances. The study does not include additional background information beyond the provided evidence.

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