This is a multi-center, open-label extension (OLE) study of approximately 800 participants with SHTG who would be rolled over from studies ISIS 678354-CS5 (NCT05079919) or ISIS 678354-CS6 (NCT05552326). Day 1 of this study may be same as the Week 53 visit of either ISIS 678354-CS5 or ISIS 678354-CS6, as applicable. Participants will receive olezarsen during the 157-week treatment period. The study will include a 31-day qualification Period, a 157-week treatment period, and a 13-week post-treatment period.