Key Inclusion Criteria:  Received bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) for ≥ 24 weeks at screening Documented plasma human immunodeficiency virus type 1 (HIV-1) ribonucleic acid (RNA) < 50 copies/mL (or undetectable HIV-1 RNA level according to the local assay being used if the limit of detection is ≥ 50 copies/mL) for ≥ 24 weeks before and at screening Plasma HIV-1 RNA < 50 copies/mL at screening  Key Exclusion Criteria:  History of prior virologic failure while receiving treatment for HIV-1 Prior use of, or exposure to, islatravir (ISL) or lenacapavir (LEN) Active, serious infections requiring parenteral therapy < 30 days before randomization Active hepatitis B virus (HBV) coinfection, defined as hepatitis B core antibody (HBcAb) positive, hepatitis B surface antigen (HBsAg) positive, or HBV deoxyribonucleic acid (DNA) positive as determined by the central laboratory  Active hepatitis C virus (HCV) coinfection, defined as detectable HCV RNA.  Note: Individuals with prior/inactive HCV infection (defined as undetectable HCV RNA) may be enrolled.  Any of the following laboratory values at screening  Creatinine clearance (CLcr) ≤ 30 mL/min according to the Cockcroft-Gault formula Clusters of differentiation 4 (CD4) T cells < 200 cells/mm^3 Individuals of childbearing potential (as defined in protocol) who have a positive serum pregnancy test at screening or positive urine and serum pregnancy tests at Day 1 prior to study drug administration Individuals who plan to continue breastfeeding during the study  Note: Other protocol defined Inclusion/Exclusion criteria may apply.