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arXiv · 2609.30571

HARDEN: Constrained Evolutionary Search for Harder, Answer-Preserving Evaluation Cases

Aditya Kumaran·Rahul Singhal·Karime Maamari·Amine Mhedhbi·Pradyumna Tambwekar
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Abstract

Language models are often evaluated on curated benchmarks that underrepresent the complexity of enterprise deployments. We introduce HARDEN, a constrained evolutionary search method to adapt the input of existing evaluation cases into more challenging variants while keeping their expected outputs fixed. HARDEN searches along generated domain-specific complexity axes while enforcing feasibility constraints such as preserving task semantics, realism, and execution validity. Across FinQA, PubMedQA, and ContractNLI and three Qwen3.5 model scales (35B-A3B, 122B-A10B, and 397B-A17B), HARDEN reduces task-model accuracy by 22.7% on average and by up to 49.9% relative to single-pass baselines using the same feasibility checks. These results show that evolutionary search can produce substantially harder valid evaluation cases.

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Aditya Kumaran, Rahul Singhal, Karime Maamari, Amine Mhedhbi, Pradyumna Tambwekar. 2026-09-24. HARDEN: Constrained Evolutionary Search for Harder, Answer-Preserving Evaluation Cases. https://arxiv.org/abs/2609.30571

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