Inclusion Criteria: - Participants who participated in double-blind placebo-controlled study (CN0120036 or CN0120037): a. Participants must have completed treatment period of parent study. - De novo participants who did not participate in double-blind placebo-controlled studies: 1. Participants must have primary diagnosis of Bipolar-I disorder established by a comprehensive psychiatric evaluation based on DSM-5-TR criteria and confirmed by the Mini International Neuropsychiatric Interview (MINI, v7.0.2), with symptoms of mania or mixed mania. 2. Participants must have Young Mania Rating Scale (YMRS) score of ≥ 14 at Screening and at baseline. 3. Participants must have CGI-BP score of ≥ 3 at Screening and at baseline. 4. Participants does not require hospitalization for acute mania. Exclusion Criteria: - Participants who participated in double-blind placebo-controlled study (CN0120036 or CN0120037): a. Discontinuation from any KarXT parent studies. - De novo participants who did not participate in double-blind placebo-controlled studies: 1. All participants with a risk for suicidal behavior at baseline as determined by Investigator's clinical assessment or history of suicidal behavior as assessed on C-SSRS. 2. Participants must not have primary diagnosis of BP-I with rapid cycling (ie, ≥ 4 distinct mood episodes in one year). 3. Participants must not have any primary DSM-5-TR disorder other than BP-I with mania or mania with mixed features within 12 months before Screening (confirmed using MINI version 7.0.2 at Screening), including BP-I with depression, (previous 3 months only), Bipolar-II disorder, major depressive disorder, and primary psychotic disorder, with the exception of mild anxiety disorders. 4. Individual has a DSM-5-TR diagnosis of moderate to severe substance use disorder (except tobacco use disorder) within the 12 months before Screening (confirmed using MINI version 7.0.2 at Screening), or current use as determined by urine toxicology screen or alcohol test. 5. Participants must not have history of irritable bowel syndrome (with or without constipation) or serious constipation requiring treatment within the last 6 months. 6. Participants must not have history or high risk of urinary retention, gastric retention, or untreated narrow-angle glaucoma. 7. Other protocol-defined Inclusion/Exclusion criteria apply.