Linbo Liu

Large reasoning models achieve strong performance on diverse tasks by producing extended chains of thought. **Self-reflection**, the ability to review and revise prior reasoning steps, is widely regarded as a key contributor to it. However, self-reflection also incurs substantial inference cost, and its governing mechanism remains underexplored. In this work, we study self-reflection through the lens of representation engineering. First, we identify a *reflection direction* in the model's latent space that separates reflection steps from non-reflection steps, and show that activation along this direction is strongly predictive of answer correctness, suggesting that self-reflection is regulated by the model's internal uncertainty. Next, building on this insight, we propose **ReflCtrl**, a framework that controls self-reflection via a *stepwise steering method*: interventions are applied only at the start of each new reasoning step, enabling fine-grained control over reflection frequency without degrading generation quality. Experiments across math and general reasoning benchmarks show that reflection is often redundant, especially in stronger models: ReflCtrl reduces total reasoning tokens by up to 33.6\% while preserving accuracy, and substantially outperforms the conventional approach which steers at every token at the same token budgets.