A Study to Evaluate the Safety and Efficacy of BGB-16673 Compared to Pirtobrutinib in Adults With Relapsed/Refractory Chronic Lymphocytic Leukemia or Small Lymphocytic Lymphoma

Inclusion Criteria: * Confirmed diagnosis of CLL or SLL, requiring treatment, based on 2018 iwCLL criteria * Previously received treatment for CLL/SLL with a covalent Bruton tyrosine kinase inhibitor (cBTKi). Patients should have disease relapsed after or refractory to at least 1 line of therapy including a cBTKi. * Participants with SLL must have measurable disease by computed tomography/magnetic resonance imaging, defined as ≥ 1 lymph node \> 1.5 cm in longest diameter and measurable in 2 perpendicular diameters. Exclusion Criteria: * Known prolymphocytic leukemia or history of, or currently suspected, Richter's transformation. * History of known bleeding disorder such as hemophilia A, hemophilia B, von Willebrand disease, or history of spontaneous bleeding requiring blood transfusion or other medical intervention * History of ischemic stroke or intracranial hemorrhage within 6 months before first dose of study drug * Prior exposure to any Bruton tyrosine kinase (BTK) protein degraders or noncovalent Bruton tyrosine kinase inhibitor (ncBTKi). * Current or history of central nervous system involvement including the brain, spinal cord, leptomeninges, and cerebrospinal fluid (as documented by imaging, cytology, or biopsy) by CLL/SLL NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.