Beyond Perfect APIs: A Comprehensive Evaluation of LLM Agents Under Real-World API Complexity

Doyoung Kim, Zhiwei Ren, Jie Hao, Zhongkai Sun, Lichao Wang +9 more
1/1/2026
cs.CLcs.AI

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Abstract

We introduce WildAGTEval, a benchmark designed to evaluate large language model (LLM) agents' function-calling capabilities under realistic API complexity. Unlike prior work that assumes an idealized API system and disregards real-world factors such as noisy API outputs, WildAGTEval accounts for two dimensions of real-world complexity: 1. API specification, which includes detailed documentation and usage constraints, and 2. API execution, which captures runtime challenges. Consequently, WildAGTEval offers (i) an API system encompassing 60 distinct complexity scenarios that can be composed into approximately 32K test configurations, and (ii) user-agent interactions for evaluating LLM agents on these scenarios. Using WildAGTEval, we systematically assess several advanced LLMs and observe that most scenarios are challenging, with irrelevant information complexity posing the greatest difficulty and reducing the performance of strong LLMs by 27.3%. Furthermore, our qualitative analysis reveals that LLMs occasionally distort user intent merely to claim task completion, critically affecting user satisfaction.

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Cite this paper

@article{kim2026beyond,
  title  = {Beyond Perfect APIs: A Comprehensive Evaluation of LLM Agents Under Real-World API Complexity},
  author = {Doyoung Kim and Zhiwei Ren and Jie Hao and Zhongkai Sun and Lichao Wang and Xiyao Ma and Zack Ye and Xu Han and Jun Yin and Heng Ji and Wei Shen and Xing Fan and Benjamin Yao and Chenlei Guo},
  year   = {2026},
  eprint = {2601.00268},
  archivePrefix = {arXiv},
  url    = {http://arxiv.org/abs/2601.00268v1}
}

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