Key Inclusion Criteria: - Participant has documented diagnosis of α-thalassemia hemoglobin H (HbH) disease (electrophoresis⎯ or high-performance liquid chromatography [HPLC]⎯based methods for Hb variant analyses are accepted), with or without transfusion dependence; compounded combination with β-thalassemia is allowed if at least 1 non-mutated β-chain gene is present. TD: i) TD participant: (1) ≥ 6 RBC units during the 24 weeks prior to randomization; and (2) No transfusion-free period for > 56 days during the 24 weeks prior to randomization; ii) NTD participant: (1) < 6 Red blood cell (RBC) units during the 24 weeks prior to randomization; and (2) RBC transfusion-free during at least 8 weeks prior to randomization; and (3) Mean baseline Hb ≤ 10 g/dL, based on a minimum of 2 measurements ≥ 1 week apart within 4 weeks prior to randomization; hemoglobin values within 21 days post-transfusion will be excluded. - Participant has Eastern Cooperative Oncology Group (ECOG) score of 0 or 1. - Investigators shall counsel women of childbearing potential (WOCBP), and male participants who are sexually active with WOCBP, on the importance of pregnancy prevention, the implications of an unexpected pregnancy, and the potential of fetal toxicity occurring due to transmission of study intervention, present in seminal fluid, to a developing fetus, even if the participant has undergone a successful vasectomy or if the partner is pregnant. Key Exclusion Criteria: - Any significant medical condition, laboratory abnormality, or psychiatric illness that would prevent the participant from participating in the study. - Any condition, including the presence of laboratory abnormalities, which places the participant at unacceptable risk if he/she were to participate in the study - History of deep venous thrombosis (DVT) or stroke requiring medical intervention ≤ 24 weeks prior to randomization - Diagnosis of α-thalassemia Trait, Hb Bart hydrops, ATRx α-thalassemia, hemoglobin S/β-thalassemia, myelodysplasia subtype anemia, or with HbE homozygous beta gene mutation. - Anemia related to nutritional deficiency, anemia of chronic disease, autoimmune hemolytic anemia, or any other hemolytic anemias (for example, severe G6PD deficiency, pyruvate kinase deficiency, etc.). - Bleeding disorders manifested by frequent bleeding episodes (e.g., menorrhagia, epistaxis, clotting disorders). - Undergone episodes of hemolysis not related to alpha-thalassemia, for example, after use of hemolysis-predisposing drugs (for example, antimalarial, nonsteroidal anti-inflammatory drug [NSAID]), within the 8 weeks prior to randomization. - Prior exposure to gene therapy to treat α-thalassemia. - Use of an erythropoiesis-stimulating agent (ESA) ≤ 24 weeks prior to randomization. Note: Other protocol-defined inclusion/exclusion criteria apply.