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)

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 needto 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 ifthey have received hepatitis B virus (HBV) antiviral therapy for at least 4 weeksand have undetectable HBV deoxyribonucleic acid (DNA) viral load beforerandomization.

• Participants with history of hepatitis C virus (HCV) infection are eligible if HCVribonucleic acid (RNA) viral load is undetectable at screening.

• Participants with human immunodeficiency virus (HIV) who meet ALL eligibilitycriteria.

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 infectionin the past 12 months before screening.

• Has clinically significant cardiovascular disease.

• Has hypersensitivity to nemtabrutinib or contraindication to ibrutinib oracalabrutinib, or any of the excipients.

• Has history of severe bleeding disorder.

• Has known additional malignancy that is progressing or has required active treatmentwithin 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 narrowtherapeutic index, cytochrome P450 3A (CYP3A) strong or moderate inducers or CYP3Astrong inhibitors.

• Received prior radiotherapy within 2 weeks of start of study intervention, orradiation-related toxicities, requiring corticosteroids.

• Received a live or live-attenuated vaccine within 30 days before the first dose ofstudy intervention. Administration of killed vaccines are allowed.

• Has received an investigational agent or has used an investigational device within 4weeks 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 ongoingsurgical complications.