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

The purpose of this study is to evaluate the efficacy and safety of tacabrutideg alone compared with pirtobrutinib in patients with relapsed or refractory (R/R) chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) who had been previously treated with a covalent Bruton tyrosine kinase inhibitor (cBTKi).

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.