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

Prior treatment

• Stroke or intracranial hemorrhage within 6 months prior to enrollment

Other illness

• Known bleeding disorders (example, von Willebrand's disease or hemophilia)
• 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

Lab values

• 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

Other

• Known or suspected Richter's transformation or central nervous system (CNS) involvement

• 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)