Body weight >= 40 kg at screening. Treated with eculizumab or ravulizumab for PNH for at least 3 months prior to Day 1. Lactate Dehydrogenase Levels =< 2x the upper limit of normal (ULN) at screening. Willingness and ability to comply with all study visits and procedures. Documented diagnosis of PNH, confirmed by high sensitivity flow cytometry. Vaccination against Neisseria meningitidis < 3 years prior to initiation of study treatment. Women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraception during the treatment period and for 6 months after the final dose of crovalimab or for 3 months after the final dose of eculizumab.
History of allogeneic bone marrow transplantation. Pregnant or breastfeeding, or intending to become pregnant during the study or within 6 months after the final dose of study treatment. Participation in another interventional treatment study with an investigational agent or use of any experimental therapy within 28 days of screening or within 5 half-lives of that investigational product, whichever was greater: participants enrolled in an eculizumab or ravulizumab interventional study are eligible provided they fulfill eligibility (e.g., are willing and able to comply with the study assessments) and stop their current trial. Positive for Active Hepatitis B and C infection (HBV/HCV). Concurrent disease, treatment, procedure, or surgery or abnormality in clinical laboratory tests that could interfere with the conduct of the study, may pose any additional risk for the participant, or would, in the opinion of the investigator, preclude the participant's safe participation in and completion of the study. History of or ongoing cryoglobulinemia at screening.