This study tests a medicine called **soticlestat**, which is added to regular anti-seizure treatments for people with Dravet Syndrome (DS) or Lennox-Gastaut Syndrome (LGS). These are conditions that cause frequent seizures. The goal is to see if soticlestat helps reduce these seizures. Participants will take soticlestat tablets along with their usual medicines. The study will last for about 4 years, with check-ups and phone calls to monitor progress.

Soticlestat was previously tested in another study (Phase 3) and will be given based on weight. The study will have a **Titration Period** where the dose is increased gradually, and a **Maintenance Period** where the dose stays the same. If needed, the dose is reduced before stopping. Participants who can't handle a low dose of 100 mg twice a day will stop the study.

• Study includes regular visits and phone follow-ups.
• Participants must have been in a previous soticlestat study.
• Individuals with certain health issues may not qualify.