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

The goal of this clinical study is to learn more about the effects of switching to the study drugs, bictegravir (BIC) plus lenacapavir (LEN), versus current therapy (Phase 2) and BIC/LEN fixed-dose combination (FDC) versus current therapy (Phase 3) in people living with HIV (PWH).

Key Inclusion Criteria: * If plasma HIV-1 RNA measurements in the 6 months prior to screening are available, all levels must be \< 50 copies/mL. * At least one documented plasma 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. * Currently receiving a complex antiretroviral (ARV) regimen due to previous viral resistance, or intolerance, or contraindication to existing single-tablet regimens (STR), and on this regimen for at least 6 months prior to the screening visit. The criteria to define a complex regimen in this study are as follows: * A regimen containing a boosted protease inhibitor or a nonnucleos(t)ide reverse transcriptase inhibitor (NRTI) plus at least 1 other third agent (ie, an agent from a class other than NRTIs) (eg, bictegravir/emtricitabine/tenofovir alafenamide (coformulated; Biktarvy®)(BVY) + darunavir/cobicistat, BVY + etravirine), or * A regimen of ≥ 2 pills/day, or a regimen requiring dosing more than once daily, or * A regimen containing parenteral agent(s) (excluding a complete long-acting injectable regimen, such as intramuscular cabotegravir plus rilpivirine) as well as oral agents. * No documented or suspected resistance to bictegravir (BIC). * Estimated glomerular filtration rate ≥ 15 mL/min according to the Cockcroft-Gault formula for creatinine clearance (CLcr) who are not on renal replacement therapy. Key Exclusion Criteria: * Prior use of, or exposure to, lenacapavir (LEN) * Active tuberculosis infection * Chronic hepatitis B virus (HBV) infection Note: Other protocol defined Inclusion/Exclusion criteria may apply.