Inclusion Criteria:  Inclusion Criteria (not all inclusive):  Subject provides written informed consent and is willing and able to comply with the protocol in the opinion of the Investigator. Subject is 18 to 65 years of age, inclusive, at the time of informed consent. Subject meets DSM-5 criteria, based on the SCID-5-CT, for bipolar I disorder, current episode depressed with or without rapid cycling disease course (≥ 4 episodes of mood disturbance but < 8 episodes in the previous 12 months) with or without psychotic features. Subject's current major depressive episode is ≥ 4 weeks and less than 12 months in duration at Screening. Subject has a MADRS total score ≥ 22 at both Screening and Baseline. Subject has a CGI-BP-S depression score ≥ 4 at both Screening and Baseline. Subject has a YMRS total score ≤ 12 at both Screening and Baseline. Subject is in good physical health, based on medical history, physical examination, neurological examination, vital signs, ECGs, and results of clinical laboratory tests (hematology, chemistry, and urinalysis).  Exclusion Criteria:  Exclusion Criteria (not all inclusive):  Subject currently has any DSM-5 defined psychiatric diagnosis other than bipolar I disorder that was the primary focus of treatment in the past 6 months prior to Screening. Subject has a lifetime history of, or symptoms consistent with, a major psychiatric diagnosis other than bipolar I disorder. These include (but are not limited to): schizophrenia, schizoaffective disorder, obsessive-compulsive disorder, or post-traumatic stress disorder. Subject has a history of non-response to an adequate (6-week) trial of 3 or more antidepressants (with or without mood stabilizers) during the current major depressive episode. Subject has any clinically significant unstable medical condition or any clinically significant chronic disease that would pose a risk to the subject or that might confound the results of the study.