Despite the remarkable synthesis capabilities of text-to-image (T2I) models, safeguarding them against content violations remains a persistent challenge. Existing safety alignments primarily focus on explicit malicious concepts, often overlooking the subtle yet critical risks of compositional semantics. To address this oversight, we identify and formalize a novel vulnerability: Multi-Concept Compositional Unsafety (MCCU), where unsafe semantics stem from the implicit associations of individually benign concepts. Based on this formulation, we introduce TwoHamsters, a comprehensive benchmark comprising 17.5k prompts curated to probe MCCU vulnerabilities. Through a rigorous evaluation of 10 state-of-the-art models and 16 defense mechanisms, our analysis yields 8 pivotal insights. In particular, we demonstrate that current T2I models and defense mechanisms face severe MCCU risks: on TwoHamsters, FLUX achieves an MCCU generation success rate of 99.52%, while LLaVA-Guard only attains a recall of 41.06%, highlighting a critical limitation of the current paradigm for managing hazardous compositional generation.
@article{arxiv.2604.15967,
title = {TwoHamsters: Benchmarking Multi-Concept Compositional Unsafety in Text-to-Image Models},
author = {Chaoshuo Zhang and Yibo Liang and Mengke Tian and Chenhao Lin and Zhengyu Zhao and Le Yang and Chong Zhang and Yang Zhang and Chao Shen},
journal= {arXiv preprint arXiv:2604.15967},
year = {2026}
}