From Tokens to Topology: When Large Language Models Meet Graph-Structured Reasoning

Qihang Zhang, Liang Zeng


Abstract
Reasoning benchmarks often collapse heterogeneous problem types into aggregate scores, obscuring which structural computations large language models (LLMs) can reliably perform. Existing graph-reasoning benchmarks cover graph traversal, broad graph computation, and graph-language interaction, but do not directly test whether graph-structured reasoning transfers across topological mechanisms under matched conditions. We introduce GraphReason-Bench (GR-Bench), comprising 1,800 programmatically generated and oracle-verified problems across three prompt-length regimes and six task families: local motif enumeration, exact-depth breadth-first search, bounded path enumeration, articulation-point identification, non-induced subgraph matching, and non-monotonic rule execution. All tasks share a text-only executable interface, exact oracles, canonical output normalization, and set-based scoring, enabling controlled cross-mechanism comparison. On the 600-instance main evaluation split across nine proprietary and open-source LLMs, we find mechanism-level dissociation: models that succeed on one structural operation often fail on others, and cross-task performance does not reduce to a stable graph-reasoning ability. Trace-level cases reveal mechanism-specific failures such as premature search termination and loss of intermediate state. An initial sparse-autoencoder probe, supported by cross-model robustness checks, shows that topology-sensitive representations become less separable as structural difficulty increases. Together, these results establish graph-structured reasoning as a measurable domain of LLM evaluation.
Anthology ID:
2026.findings-emnlp.1826
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
38990–39012
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1826/
DOI:
Bibkey:
Cite (ACL):
Qihang Zhang and Liang Zeng. 2026. From Tokens to Topology: When Large Language Models Meet Graph-Structured Reasoning. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 38990–39012, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
From Tokens to Topology: When Large Language Models Meet Graph-Structured Reasoning (Zhang & Zeng, Findings 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.findings-emnlp.1826.pdf