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ComplexFuncBench

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Progress Over Time

Interactive timeline showing model performance evolution on ComplexFuncBench

State-of-the-art frontier
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ComplexFuncBench Leaderboard

7 models
ContextCostLicense
1
OpenAI
OpenAI
—128K$2.50 / $10.00
2
OpenAI
OpenAI
—1.0M$2.00 / $8.00
3—1.0M$0.33 / $2.75
4
OpenAI
OpenAI
———
5—1.0M$0.40 / $1.60
6
OpenAI
OpenAI
———
7—1.0M$0.10 / $0.40
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About this benchmark

What is ComplexFuncBench?

ComplexFuncBench is a benchmark designed to evaluate large language models' capabilities in handling complex function calling scenarios. It encompasses multi-step and constrained function calling tasks that require long-parameter filling, parameter value reasoning, and managing contexts up to 128k tokens. The benchmark includes 1,000 samples across five real-world scenarios.

ComplexFuncBench is a text benchmark evaluating models on long context, reasoning, structured output, and tool calling tasks. LLM Stats tracks 7 models on this benchmark, scored on a 0–1 scale. The current average is 0.5, with the leader at 0.7.

Compare leaders on the best AI for long context, best AI for reasoning, best AI for structured output and best AI for tool calling leaderboards.

Current leaders

GPT-4o from OpenAI currently leads the ComplexFuncBench leaderboard with a score of 0.665 across 7 evaluated AI models.

1GPT-4oOpenAI66.5%
2GPT-4.1OpenAI65.5%
3Nova 2 SonicAmazon65.2%

Source paper

Title
ComplexFuncBench: Exploring Multi-Step and Constrained Function Calling under Long-Context Scenario
Authors
Lucen Zhong, Zhengxiao Du, Xiaohan Zhang, Haiyi Hu, and 1 others
Published
Abstract

Enhancing large language models (LLMs) with real-time APIs can help generate more accurate and up-to-date responses. However, evaluating the function calling abilities of LLMs in real-world scenarios remains under-explored due to the complexity of data collection and evaluation. In this work, we introduce ComplexFuncBench, a benchmark for complex function calling across five real-world scenarios. Compared to existing benchmarks, ComplexFuncBench encompasses multi-step and constrained function calling, which requires long-parameter filing, parameter value reasoning, and 128k long context. Additionally, we propose an automatic framework, ComplexEval, for quantitatively evaluating complex function calling tasks. Through comprehensive experiments, we demonstrate the deficiencies of state-of-the-art LLMs in function calling and suggest future directions for optimizing these capabilities. The data and code are available at \url{https://github.com/THUDM/ComplexFuncBench}.

FAQ

Common questions about the ComplexFuncBench benchmark and leaderboard.

What is the ComplexFuncBench benchmark?

ComplexFuncBench is a benchmark designed to evaluate large language models' capabilities in handling complex function calling scenarios. It encompasses multi-step and constrained function calling tasks that require long-parameter filling, parameter value reasoning, and managing contexts up to 128k tokens. The benchmark includes 1,000 samples across five real-world scenarios.

What is the ComplexFuncBench leaderboard?

The ComplexFuncBench leaderboard ranks 7 AI models based on their performance on this benchmark. Currently, GPT-4o by OpenAI leads with a score of 0.665. The average score across all models is 0.475.

What is the highest ComplexFuncBench score?

The highest ComplexFuncBench score is 0.665, achieved by GPT-4o from OpenAI.

How many models are evaluated on ComplexFuncBench?

7 models have been evaluated on the ComplexFuncBench benchmark, with 0 verified results and 7 self-reported results.

Where can I find the ComplexFuncBench paper?

The ComplexFuncBench paper is available at https://arxiv.org/abs/2501.10132. The paper details the methodology, dataset construction, and evaluation criteria.

What categories does ComplexFuncBench cover?

ComplexFuncBench is categorized under long context, reasoning, structured output, and tool calling. The benchmark evaluates text models.

Which model offers the best value on ComplexFuncBench?

Among models scoring within 10% of the leader, Nova 2 Sonic from Amazon is the cheapest, at $0.33 per million input tokens with a score of 0.652.

How recent are the ComplexFuncBench leaderboard results?

The ComplexFuncBench leaderboard was last updated in October 2026 and currently includes 7 evaluated models.