# When2Think: Learning Difficulty-Aware Length Control for Efficient Hybrid Reasoning Models > Source: > Published: 2026-09-18 03:00:08+00:00 Large Reasoning Models (LRMs) achieve strong performance on complex tasks but exhibit systematic inefficiency: they often overthink easy problems and underthink hard ones. Existing approaches based on uniform length penalties or rigid routing incur an efficiency tax, trading reduced computation on e