The digital transformation of everyday consumption has prompted platforms to quantify pro-environmental behavior through gamification, yet how such quantification affects the continuance of green consumption remains poorly understood. Existing research on the quantified self has concentrated on self-oriented domains such as health and efficiency, with little attention to its role in prosocial green consumption or to the difference between competitive and non-competitive quantification. Drawing on social identity theory, this study uses two scenario-based online experiments to examine how quantified self orientation shapes consumers’ intention to continue green consumption and the underlying mechanism. Experiment 1 (competitive vs. non-competitive quantified self, between-subjects) tests the main effect and the mediating role of symbolic behavioral motivation; Experiment 2 (2 × 2 between-subjects) introduces in-group versus out-group contexts as a moderator. The results show that, relative to non-competitive quantification, competitive quantification elicits stronger continuance intention and self-rated behavioral intensity; symbolic behavioral motivation partially mediates this effect; and group context moderates the relationship between symbolic motivation and green consumption, amplifying it in the in-group and attenuating it in the out-group. By extending the quantified self from self-oriented to prosocial settings, the study delineates an instrument–motivation–context pathway and informs the design of gamified, identity-based interventions for sustainable consumption.