Objective: To assess the feasibility, acceptability, and preliminary effects of circadian rhythm for sleep (CRS), a mobile digital therapeutic that delivers closed-loop, wearable- and light-sensor–driven circadian coaching for insomnia. Methods: Six-week, single-arm feasibility study in adults with short-term or chronic insomnia. CRS provided daily recommendations emphasizing stable wake-up time, morning light exposure, and daytime activity. Feasibility and acceptability outcomes were assessed (completion, passive-sensor data capture/adherence, satisfaction), and the primary clinical outcome (exploratory) was change in Insomnia Severity Index (ISI) from baseline to Week 6; the key secondary clinical outcome (exploratory) was Pittsburgh Sleep Quality Index (PSQI). Objective sleep–wake metrics from wearable device were explored. Results: Twenty-three participants were enrolled; 20 completed the program (87.0%), and 16 comprised the prespecified analysis set based on data-fidelity criteria. Among these 16 participants, valid passive sensor data from the wearable and light sensors were captured on 88.6% of study days. ISI significantly improved from baseline to Week 6 (median 21.0 → 14.0; p < .001 by within-subject analysis), and PSQI improved (mean 10.9 → 7.7; p < .001; partial η ² ≈ 0.50). Objective wearable metrics (total sleep time, time-in-bed, sleep onset, wake time) did not change significantly over time in this short pilot. Satisfaction was favorable (mean 37.9/45). No adverse events occurred. Conclusions: CRS was feasible and acceptable, and was associated with within-subject improvements in subjective insomnia symptoms in this single-arm feasibility study; however, because there was no control group, these findings are preliminary and hypothesis-generating, supporting further evaluation in larger randomized controlled trials. Trial registry name: Clinical Research Information Service URL: https://cris.nih.go.kr Trial registration number: KCT0010801

This study explored the latent profiles of psychological flexibility and inflexibility, core processes in acceptance and commitment therapy (ACT). Psychological flexibility refers to the capacity to stay open to internal experiences and to pursue valued actions even in the presence of distress, whereas inflexibility involves rigid attempts to avoid or control them. Using a subgroup-based approach within a nomothetic framework, we investigated how the identified subgroups were associated with depression and anxiety. Participants comprised 1,000 Korean young adults (M_age = 28.68, SD_age = 4.10). Latent profile analysis was conducted alongside the Bolck-Croon-Hagenaars (BCH) method to identify distinct profiles. Three latent profiles of ACT processes emerged (i.e. high flexibility, moderate flexibility, high inflexibility). Women were more likely to be classified in the high inflexibility profile. Participants in the high flexibility profile reported lower levels of depression and anxiety, whereas those in the high inflexibility profile had more severe symptoms. Interestingly, unexpected findings were obtained regarding experiential avoidance. The identification of distinct profiles suggests that psychological flexibility and inflexibility may be more polarized in the study sample, with individuals clustering into either adaptive or maladaptive coping styles. Cultural factors may also play a role in shaping the function and impact of experiential avoidance.