Evaluating LLM Agents Beyond Local Edit Validity

Kunhee Ryu, Chi-Guhn Lee, Keeheon Lee


Abstract
Evaluations of sequential large language model (LLM) agents often report local action validity or final success. Delayed constructive tasks additionally require recoverability, meaning each accepted edit must leave the partial artifact completable within the remaining budget. We introduce a measurement protocol across Word Ladder, an alloy composition proxy, and the fitness landscape of the B1 domain of protein G (GB1). We call an episode surface clean when every action is well formed and locally admissible. Across six models, Word Ladder exposes interface failure with 36.1% local validity. Alloy and GB1 episodes are often surface clean, yet only 16.0% and 6.8% of them succeed. Exact enumeration of 625 GB1 variants over budgets from zero to six decomposes failure. Among surface clean episodes, 51.4% cross a recoverability boundary, while 14.1% of the remaining episodes succeed. Bounded composition audits and intervention checks connect bottlenecks to repair classes. These results establish recoverability as a decomposable and auditable evaluation axis that informs interventions for sequential agents.
Anthology ID:
2026.findings-emnlp.893
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:
18910–18944
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.893/
DOI:
Bibkey:
Cite (ACL):
Kunhee Ryu, Chi-Guhn Lee, and Keeheon Lee. 2026. Evaluating LLM Agents Beyond Local Edit Validity. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 18910–18944, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Evaluating LLM Agents Beyond Local Edit Validity (Ryu et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.893.pdf