An Open-label Extension Trial of CVL-865 as Adjunctive Therapy in the Treatment of Focal Onset Seizures

* Participants who completed treatment in Trial CVL-865-SZ-001 (NCT04244175) * A female participant of childbearing potential who is sexually active with a nonsterilized male partner must agree to use a highly effective method of contraception from signing of informed consent through 30 days post last dose * A male participant with a pregnant or a nonpregnant partner of childbearing potential must agree to use a condom during treatment and until the end of relevant systemic exposure in the male participant for 94 days following the last dose with the investigational medicinal product (IMP) * Participants who are capable of giving signed informed consent * Participants who are able, in the opinion of the investigator, to understand the nature of the trial and comply with protocol requirements, including the prescribed dosage regimens, scheduled visits, laboratory tests, and other trial procedures

* Participants who, in the opinion of the investigator, medical monitor, or sponsor, should not participate in the trial * Participants who, in the judgment of the investigator, experienced poor tolerability to the IMP during the double-blind trial or whose safety assessments resulted in new concerns that would suggest that the participant may not be appropriate for 57 weeks of treatment with CVL-865 in an extension trial * Participants who experienced status epilepticus during Trial CVL-865-SZ-001 * Participants who have demonstrated substantial noncompliance to trial procedures in Trial CVL-865-SZ-001, based on the investigator's judgment, would not be eligible for this trial * Participants who answer "yes" on the C-SSRS Suicidal Ideation Item 4 or Item 5 (Active Suicidal Ideation with Some Intent to Act, Without Specific Plan, or Active Suicidal Ideation with Specific Plan and Intent), or participants who answer "yes" on any of the 5 C-SSRS Suicidal Behavior Items (actual attempt, interrupted attempt, aborted attempt, preparatory acts, or behavior), or participants who, in the opinion of the investigator, present a serious risk of suicide * Participants with any of the following abnormalities in clinical laboratory tests at Visit 1, as assessed by the central laboratory and confirmed by a single repeat measurement, if deemed necessary (Females: Hemoglobin \<11 gram per deciliter (g/dL); Males: hemoglobin \<12 g/dL; White blood cell (WBC) count \<3.0 x 10 power 9 per liter (10\^9/L); Neutrophil count \<2.0 x 10\^9/L; Platelet count \<150 × 10\^9/L) * Participants who would be likely to require the use of prohibited concomitant medications during the trial * Female participants who have a positive pregnancy test result