A Clinical Trial to Determine the Long-term Safety and Tolerability of an Investigational Drug in People With Major Depressive Episode Associated With Bipolar I Disorder (Bipolar I Depression).

Inclusion Criteria:

• Subject provides written informed consent and is willing and able to comply with theprotocol in the opinion of the Investigator.

• Subject has completed 6 weeks of double-blind treatment and all scheduledassessments from Visit 6/EOT (Day 42) of the lead-in study of SEP-4199 CR.

• Subject is medically appropriate for long-term open-label treatment with SEP-4199 CRin the opinion of the Investigator.

• Female subjects of childbearing potential must agree to use effective and reliablecontraception throughout the study and for at least 30 days after the last dose ofstudy drug has been taken. In the Investigator's judgment, the subject will adhereto this requirement.

• Male subjects agree to avoid fathering a child and to use effective methods of birthcontrol throughout the study and until at least 90 days after the last study drugadministration.

Exclusion Criteria:

• Subject is at high risk of non-compliance in the opinion of the Investigator.

• Subject plans to initiate treatment with a prohibited psychotropic medication duringthe study.

• Subject plans to initiate treatment with transcranial magnetic stimulation (TMS),electroconvulsive therapy (ECT), vagus nerve stimulation (VNS), or deep brainstimulation (DBS) during the study.

• Subject experienced a moderate or severe hyperprolactinemia-related AESI in thelead-in study of SEP-4199 CR.

• Subject will require treatment with a drug that is associated with increases in QTcinterval.

• Subject had any of the following at Visit 6/EOT (Day 42) of the lead-in study ofSEP-4199 CR based on machine reading:

• increase in QTcF interval of ≥ 30 msec AND a QTcF interval ≥ 480 msec, from baselineof the lead-in study of SEP-4199 CR AND a QTCF interval ≥ 480msec

• increase in QTcF interval ≥ 60 msec, from baseline of the lead-in study of SEP-4199CR

• QTcF interval ≥ 500 msec

• treatment-emergent clinically significant ECG abnormality.

• Subject is considered by the Investigator to be at imminent risk of suicide orinjury to self or others, has a MADRS item 10 (suicidal ideation) score ≥ 4, oranswers "yes" to "suicidal ideation" item 4 (active suicidal ideation with someintent to act, without specific plan) or item 5 (active suicidal ideation withspecific plan and intent) on the C-SSRS assessment at Visit 6/EOT (Day 42) of thelead-in study of SEP-4199 CR.

• Female subject of childbearing potential, has a positive urine pregnancy test atVisit 6/EOT (Day 42) of the lead-in study of SEP-4199 CR or plans to become pregnantduring the current study.

• Subject tests positive for any drug of abuse or cannabis at Visit 6/EOT (Day 42) ofthe lead-in study of SEP-4199 CR