A Study Evaluating the Efficacy and Safety of ABP 959 Compared With Eculizumab in Adult Participants With PNHDAHLIA

- Men and women ≥ 18 years of age. - Historical diagnosis of PNH. - Administration of eculizumab for ≥ 6 months and currently receiving 900 mg of eculizumab. - Hemoglobin ≥ 9.0 g/dL for at least 6 weeks before randomization. - Lactate dehydrogenase < 1.5 × the upper limit of normal at screening. - Platelet count ≥ 50 × 10^9/L. - Absolute neutrophil count (ANC) ≥ 0.5 x 10^9/L (500/μL). - Participants must be vaccinated against Neisseria meningitidis. - Participants must sign an IRB/IEC-approved ICF before participation in any procedures.

- Known or suspected hereditary complement deficiency. - Clinically significant cardiovascular disease (including myocardial infarction, unstable angina, symptomatic congestive heart failure [New York Heart Association ≥ Class III], serious uncontrolled cardiac arrhythmia), peripheral vascular disease, cerebrovascular accident, or transient ischemic attack in the previous 6 months. - Evidence of acute thrombosis (liver Doppler ultrasound of hepatic and portal veins). - Known to be positive for human immunodeficiency virus. - Woman who is pregnant or breastfeeding. - Participant is currently enrolled in or has not yet completed at least 30 days since ending other investigational device or drug study(s), or participant is receiving other investigational agent(s). - Participant has known sensitivity to any of the products to be administered during the study, including mammalian cell-derived drug products. - History of meningococcal infection. - Presence or suspicion of active bacterial infection, or recurrent bacterial infection. - History of bone marrow transplantation. - Red blood cell transfusion required within 12 weeks before randomization. - Participant experienced ≥ 2 breakthrough events, (ie, signs and symptoms of intravascular hemolysis, that require dose and/or schedule adjustments of eculizumab) in the previous 12 months before screening.