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 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.