A Study of Nemtabrutinib (MK-1026) Versus Comparator (Investigator's Choice of Ibrutinib or Acalabrutinib) in First Line (1L) Chronic Lymphocytic Leukemia (CLL)/ Small Lymphocytic Lymphoma (SLL) (MK-1026-011/BELLWAVE-011)

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.

Inclusion Criteria: The main inclusion criteria include but are not limited to the following: * Confirmed diagnosis of CLL/SLL and active disease clearly documented to have a need to initiate therapy. * Has at least 1 marker of disease burden. * Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2 within 7 days before randomization. * Has the ability to swallow and retain oral medication. * Participants who are hepatitis B surface antigen (HBsAg) positive are eligible if they have received hepatitis B virus (HBV) antiviral therapy for at least 4 weeks and have undetectable HBV deoxyribonucleic acid (DNA) viral load before randomization. * Participants with history of hepatitis C virus (HCV) infection are eligible if HCV ribonucleic acid (RNA) viral load is undetectable at screening. * Participants with human immunodeficiency virus (HIV) who meet ALL eligibility criteria. Exclusion Criteria: The main exclusion criteria include but are not limited to the following: * Has an active hepatitis B virus/ hepatitis C virus (HBV/HCV) infection. * Has gastrointestinal (GI) dysfunction that may affect drug absorption. * Has diagnosis of Richter Transformation or active central nervous system (CNS) involvement by CLL/SLL. * Has had acquired immune deficiency syndrome (AIDS)-defining opportunistic infection in the past 12 months before screening. * Has clinically significant cardiovascular disease. * Has hypersensitivity to nemtabrutinib or contraindication to ibrutinib or acalabrutinib, or any of the excipients. * Has history of severe bleeding disorder. * Has known additional malignancy that is progressing or has required active treatment within the past 2 years. * Has received any systemic anticancer therapy for CLL/SLL. * Is currently being treated with p-glycoprotein (P-gp) substrates with a narrow therapeutic index, cytochrome P450 3A (CYP3A) strong or moderate inducers or CYP3A strong inhibitors. * Received prior radiotherapy within 2 weeks of start of study intervention, or radiation-related toxicities, requiring corticosteroids. * Received a live or live-attenuated vaccine within 30 days before the first dose of study intervention. Administration of killed vaccines are allowed. * Has received an investigational agent or has used an investigational device within 4 weeks before study intervention administration. * Has active infection requiring systemic therapy, including intravenous (IV) antibiotics during screening. * Participants who have not adequately recovered from major surgery or have ongoing surgical complications.