Study to Evaluate the Safety and Efficacy of Switching From Regimens Consisting of Boosted Atazanavir or Darunavir Plus Either Emtricitabine/Tenofovir or Abacavir/Lamivudine to Bictegravir/Emtricitabine/Tenofovir Alafenamide in Virologically Suppressed HIV-1 Infected Adults

Key Inclusion Criteria:

• Currently receiving a once daily antiretroviral regimen consisting of ritonavir or cobicistat boosted ATV or DRV plus either FTC/TDF or ABC/3TC for ≥ 6 months preceding the screening visit
• Adequate renal function:

• Estimated glomerular filtration rate ≥ 50 mL/min (≥ 0.83 mL/sec) according to the Cockcroft-Gault formula
• Life expectancy ≥ 1 year
• Currently on a stable regimen for ≥ 6 months preceding the screening visit with documented plasma HIV-1 RNA < 50 copies/mL for ≥ 6 months preceding the screening visit (or undetectable HIV-1 RNA level according to the local assay being used if the limit of detection is ≥ 50 copies/mL). Prior changes in antiretroviral regimen are only allowed due to tolerability issues or for regimen simplification. Unconfirmed virologic elevations of ≥ 50 copies/mL (transient detectable viremia, or "blip") prior to screening are acceptable. (If the lower limit of detection of the local HIV-1 RNA assay is < 50 copies/mL [e.g., < 20 copies/mL], the plasma HIV-1 RNA level cannot exceed 50 copies/mL on two consecutive HIV-1 RNA tests)
• Have no documented or suspected resistance to FTC, tenofovir, ABC or 3TC, including but not limited to the reverse transcriptase resistance mutations K65R and M184V/I
• No previous use of any approved or experimental integrase strand transfer inhibitor (INSTI)

Key Exclusion Criteria:

• An opportunistic illness indicative of stage 3 HIV diagnosed within the 30 days prior to screening
• Individuals experiencing decompensated cirrhosis (eg, ascites, encephalopathy, or variceal bleeding)
• Have been treated with immunosuppressant therapies or chemotherapeutic agents within 3 months of study screening, or expected to receive these agents or systemic steroids during the study (eg, corticosteroids, immunoglobulins, and other immune- or cytokine based therapies)
• Current alcohol or substance use judged by the Investigator to potentially interfere with subject study compliance
• A history of or ongoing malignancy (including untreated carcinoma in-situ) other than cutaneous Kaposi's sarcoma (KS), basal cell carcinoma, or resected, non-invasive cutaneous squamous carcinoma. Individuals with biopsy-confirmed cutaneous KS are eligible, but must not have received any systemic therapy for KS within 30 days of Day 1 and are not anticipated to require systemic therapy during the study
• Active, serious infections (other than HIV 1 infection) requiring parenteral antibiotic or antifungal therapy within 30 days prior to Day 1
• Participation in any other clinical trial, including observational studies, without prior approval from the sponsor is prohibited while participating in this trial
• Any other clinical condition or prior therapy that, in the opinion of the Investigator, would make the individual unsuitable for the study or unable to comply with the dosing requirements
• Any known allergies to the excipients of B/F/TAF FDC or ATV, RTV, DRV, COBI, FTC/TDF or ABC/3TC
• Females who are pregnant (as confirmed by positive serum pregnancy test)
• Females who are breastfeeding
• Acute hepatitis in the 30 days prior to study entry
• Chronic hepatitis B infection in individuals not on a TDF containing regimen, as determined by either:

• Positive hepatitis B virus (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
• Active tuberculosis infection

Note: Other protocol defined Inclusion/Exclusion criteria may apply.