The goal of this study is to evaluate nemtabrutinib compared with investigator's choice of ibrutinib or acalabrutinib in participants with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) who have not received any prior therapy. The primary hypotheses are that (1) nemtabrutinib is non-inferior to ibrutinib or acalabrutinib with respect to objective response rate (ORR) per International Workshop on Chronic Lymphocytic Leukemia (iwCLL) Criteria 2018 by blinded independent central review (BICR) and (2) nemtabrutinib is superior to ibrutinib or acalabrutinib with respect to progression free survival (PFS) per iwCLL Criteria 2018 by BICR.