Study to Compare Bictegravir/Lenacapavir Versus Current Therapy in People With HIV-1 Who Are Successfully Treated With Biktarvy

Key Inclusion Criteria: * Currently receiving B/F/TAF for at least 6 months prior to screening. * If plasma human immunodeficiency virus type 1 (HIV-1) ribonucleic acid (RNA) measurements in the last 6 months prior to screening are available, all levels must be \< 50 copies/mL. * At least one documented HIV-1 RNA level measured between 6 and 12 months (± 2 months) prior to screening. This and any other HIV-1 RNA measurements documented in this period must be \< 50 copies/mL. * Plasma HIV-1 RNA levels \< 50 copies/mL at screening. * No documented or suspected resistance to BIC (including integrase strand-transfer inhibitor resistant (INSTI-R) mutations T66A/I/K, E92G/Q, G118R, F121Y, Y143C/H/R, S147G, Q148H/K/R, N155H/S, or R263K in the integrase gene). * No documented or suspected resistance to tenofovir alafenamide (TAF) (TAF; mutations K65R, K65N, K70E, Q151M or T69 insertion, or ≥ 3 of the following thymidine analog mutations \[M41L, D67N, K70R, L210W, T215Y/F, K219Q/E/N/R\] in the reverse transcriptase gene). * Estimated glomerular filtration rate ≥ 30 mL/min according to the Cockcroft-Gault formula for creatinine clearance. Key Exclusion Criteria: * Positive serum pregnancy test or pregnant at screening or a positive pregnancy test prior to Day 1 randomization. * Breastfeeding (nursing). * Prior use of, or exposure to, LEN. * Active, serious infections (other than HIV-1) requiring parenteral therapy \< 30 days prior to randomization. * Active tuberculosis infection. * Acute hepatitis \< 30 days before randomization. * Chronic hepatitis B virus (HBV) infection, as determined by either: * Positive HBV surface antigen and negative HBV surface antibody, regardless of HBV core antibody status, at the screening visit. * Positive HBV core antibody and negative HBV surface antibody, regardless of HBV surface antigen status, at the screening visit. * Known hypersensitivity to the study drug, its metabolites, or any formulation excipient. * History of or current clinical decompensated liver cirrhosis (eg, ascites, encephalopathy, or variceal bleeding). * Abnormal electrocardiogram (ECG) at the screening visit that is clinically significant as determined by the investigator. * Active malignancy requiring acute systemic therapy. * Any of the following laboratory values at screening: * Alanine aminotransferase \> 5 × upper limit of normal (ULN). * Direct bilirubin \> 1.5 × ULN. * Platelets \< 50,000/mm\^3. * Hemoglobin \< 8.0 g/dL. * Requirement for ongoing therapy with or prior use of any prohibited medications listed in the protocol. * Participation or planned participation in any other clinical study (including observational studies) without prior approval from the sponsor. * Any other clinical condition or prior therapy that, in the opinion of the investigator, would make the participant unsuitable for the study or unable to comply with dosing requirements. Note: Other protocol defined Inclusion/Exclusion criteria may apply.