Reward prospect modulates cognitive control, promoting either more stable or more flexible behavior depending on the immediate reward history: Previous studies have shown that specifically remaining high reward prospect enhances stability, as reflected by reduced voluntary task switching. However, it remains unclear whether sequential changes in expected reward magnitude influence only conscious control processes or also affect behavioral stability without explicit awareness of these changes. In this study (n=42), we used a voluntary task-switching paradigm with cues announcing varying reward prospects. However, the meanings of the cues, indicating either high or low reward magnitude, were not explicitly instructed to participants. Results showed that participants nevertheless learned the cue meanings, as they responded faster on high-reward trials than on low-reward trials. In addition, sequential changes in reward prospect influenced behavioral stability, with participants switching tasks less frequently, specifically on "remain high" trials. These findings confirm previous results with explicitly instructed reward cues, but suggest that cue meanings can be acquired implicitly, as participants were unable to report them verbally.