When2Think: Difficulty-aware length control for hybrid reasoning (arXiv:2609.19671v1)
When2Think is a post-training framework that adaptively allocates computation in hybrid reasoning models by introducing Instance-level Difficulty-Aware Control (IDAC), a reward-shaping mechanism that uses precomputed reference statistics and verifier-based rewards to decide when to answer directly versus continue multi-step reasoning. On mathematical benchmarks, the paper reports efficiency gains—e.g., on AIME24 Pass@3 up 10.0% with 27.9% fewer tokens versus the base model, and on AIME25 achieves 40.0% Pass@3, outperforming compression- and routing-only baselines.