This study is for adults with chronic spontaneous urticaria (CSU), a skin condition causing itchy hives, that is not controlled by second generation H1-antihistamines (sgH1-AH). It compares two treatments: remibrutinib, a pill taken twice daily, and dupilumab, an injection given every two weeks. The study lasts up to 24 weeks, starting with a screening period of up to 4 weeks to check eligibility, followed by a 12-week treatment period. After this, there is an optional open-label extension for 12 more weeks if remibrutinib is not available for sale yet.

• The study involves several visits over 24 weeks, including possible safety follow-ups.
• Participants will receive either remibrutinib or dupilumab as additional treatment.
• Participants must not have serious health issues like heart disease or uncontrolled high blood pressure.

Participants must be willing to keep a daily diary and follow the study's rules. They should not have used similar medicines before. This study hopes to find out which treatment works better for CSU at earlier stages.