There is much evidence that the prospect of reward modulates cognitive control in terms of more stable behavior. Increases in expected reward magnitude, however, have been suggested to increase flexible behavior as evidenced by reduced switch costs. In a series of experiments, the authors provide evidence that this increased cognitive flexibility following increases in reward magnitude also promotes deliberate task switching. A modified task switching paradigm with forced- and free-choice trials and varying reward prospects was used. In Experiments 1-3 the prospect of a reward increase as compared to unchanged high reward increased voluntary switching rate (VSR). Experiment 4 showed that the prospect of a reward decrease did not alter VSR as compared to unchanged low reward. Experiment 5 used a standard voluntary task switching procedure and confirmed VSR effects found in Experiments 1-4. These findings are strong evidence for a mechanism that biases the cognitive system either toward stability or flexibility depending on changing reward expectation. Results are discussed within the framework of the adaptive gain theory.