A Study of Rapastinel for Rapid Treatment of Depression and Suicidality in Major Depressive Disorder

* Meet Diagnostic and Statistical Manual of Mental Disorders - Fifth Edition (DSM-5) criteria for MDD * Current major Depressive episode of at least 4 weeks and not exceeding 24 months in duration at visit 1 * Have current, ongoing suicidality (ideation or behavior) of sufficient severity to warrant hospitalization based on the judgment of the investigator * If female of childbearing potential, have a negative serum β-human chorionic gonadotropin (β-hCG) pregnancy test.

* DSM-5-based diagnosis of any disorder other than MDD that was the primary focus of treatment within 1 month before Visit 1. * Lifetime history or currently meet DSM-5 criteria for: 1. Schizophrenia spectrum or other psychotic disorder 2. Bipolar or related disorder 3. Major neurocognitive disorder 4. Neurodevelopmental disorder of greater than mild severity or of a severity that impacts the participant's ability to consent, follow study directions, or otherwise safely participate in the study. 5. Dissociative disorder 6. Posttraumatic stress disorder 7. MDD with psychotic features * Significant homicidal ideation or at imminent risk of injuring others or causing significant damage to property, as judged by the investigator. * Prior participation in any investigational study of rapastinel/GLYX-13