An Open-label Study of XEN1101 in Epilepsy

Inclusion Criteria: 1. Subject must be properly informed of the nature and risks of the study and give informed consent in writing prior to entering the study (for adult subjects) and for adolescent subject's parent/legal guardian and subject gives informed consent or assent in writing prior to entering the study. 2. Subject must have successfully completed the double-blind treatment period (DBP) and have not terminated early from Study X-TOLE2, X-TOLE3, or X-ACKT, met all eligibility requirements, and had no important protocol deviations (in the opinion of the sponsor) or adverse events (AEs) (in the opinion of the investigator) that would preclude the subject's entry into the long-term extension study. 3. In the opinion of the investigator, the subject is able to understand verbal and written instructions and will adhere to all study schedules and requirements. 4. Subject is able to keep accurate seizure diaries. Exclusion Criteria: 1. Subject met any of the withdrawal criteria while in Study X-TOLE2, X-TOLE3, or X-ACKT. 2. Subject has any medical condition, personal circumstance, or ongoing AE (from Study X-TOLE2, X-TOLE3, or X-ACKT) that, in the opinion of the investigator, exposes the subject to unacceptable risk by participating in the study, or prevents adherence to the protocol. 3. Subject is planning to enter a clinical study with a different investigational drug or planning to use any experimental device for treatment of epilepsy or any other medical condition during the study and until 28 days after completion of this study.