Studying dynamic patterns among grandiose and vulnerable narcissistic states has become an important area of inquiry. The g-FLUX (Oltmanns & Widiger, 2018) scale is a 9-item self-report measure designed to capture narcissistic dynamics in the absence of intensive longitudinal designs (e.g., ambulatory assessment, ecological momentary assessment). Though this scale has been associated with dispositional measures of narcissism, it has not yet been validated using ambulatory methods that can directly assess fluctuation in narcissistic states. The present study examined whether the g-FLUX scale predicts variability in state grandiosity and vulnerability across two samples: a community sample ( = 320) that was oversampled for low modesty and an independent undergraduate sample ( = 314). Results revealed that the g-FLUX scale predicts momentary variability in grandiosity and vulnerability. Results were stronger in the community sample. The study suggests that researchers should consider using the g-FLUX scale when interested in capturing dynamics within narcissism, especially when intensive longitudinal designs (e.g., ambulatory assessment methods) are not an option. (PsycInfo Database Record (c) 2021 APA, all rights reserved).