--- - |2+ Abstract Objective Research examining relationships between trait openness to experience, psychopathology, and well‐being has produced contradictory findings. Examining temporary manifestations of openness may provide further insight into the interplay between openness and symptoms in clinical populations. Method The present study validated a brief new measure to assess daily openness in 271 adults (Mage = 34 years old, 52% women, 83% White) taking part in seven days of intensive treatment for acute psychopathology. Participants also completed a daily measure of depressive symptoms. Results Participants overall experienced a significant but small increase in daily openness during treatment. Two latent classes best characterized initial levels and trajectories of openness in this sample: medium/increase (86% of sample) and low/decrease (14%). Daily openness negatively related to depressive symptoms over the entire course of treatment and at the daily level. Daily openness however did not predict depressive symptoms from one day to the next (or vice‐versa). Conclusions Results of this study contribute to the scientific understanding of positive personality change during challenging life circumstances. Future research could examine whether targeting openness as part of treatment holds clinical value. Findings are limited by this study's short timeframe and the lack of ethnoracial diversity in this sample. This article is protected by copyright. All rights reserved. - Journal of Personality, Volume 0, Issue ja, -Not available-.