A Study to Customize Ibrutinib Treatment Regimens for Participants With Previously Untreated Chronic Lymphocytic Leukemia

Inclusion Criteria

• Diagnosis of chronic lymphocytic leukemia/ small lymphocytic lymphoma (CLL/SLL) as per International Workshop on Chronic Lymphocytic Leukemia (iwCLL) 2018 diagnostic criteria
• For ibruinib + venetocIax (I+V) cohorts: eastern cooperative oncology group (ECOG) performance status of 0-1. For ibrutinib monotherapy cohorts: ECOG performance status of 0-2
• Measurable nodal disease by computed tomography (CT), defined as at least 1 lymph node greater than and equal to (>=) 1.5 centimeters (cm) in longest diameter
• A participant using oral contraceptives must use an additional contraceptive method
• A participant must agree not to be pregnant, breastfeeding, or planning to become pregnant while enrolled in this study or until 1 month after last dose or per local label if more conservative (for example, 3 months in European Union or Canada and 1 month in United States)

Exclusion Criteria

• Uncontrolled autoimmune hemolytic anemia or idiopathic thrombocytopenia purpura, such as those participants with a declining hemoglobin level or platelet count secondary to autoimmune destruction within the 4 weeks prior to first dose of study treatment, or the need for prednisone greater than (>) 20 milligrams (mg) daily (or corticosteroid equivalent) to treat or control the autoimmune disease
• Known bleeding disorders (example, von Willebrand's disease or hemophilia)
• Stroke or intracranial hemorrhage within 6 months prior to enrollment
• Known or suspected Richter's transformation or central nervous system (CNS) involvement
• Currently active, clinically significant cardiovascular disease, such as uncontrolled arrhythmia or Class II, III, or IV congestive heart failure as defined by the New York Heart Association Functional Classification