Study of Bictegravir/Emtricitabine/Tenofovir Alafenamide Fixed Dose Combination in Adolescents and Children With Human Immunodeficiency Virus-1

The goals of this clinical study are to learn how Bictegravir/Emtricitabine/Tenofovir Alafenamide fixed dose combination (FDC) interacts with the body, confirm the dose, and also to learn more about the safety and tolerability of Bictegravir/Emtricitabine/Tenofovir Alafenamide FDC in adolescents and children with HIV-1.

Key Inclusion Criteria: Cohort 1: HIV-1 infected adolescents (12 to \< 18 years of age and screening weight ≥ 35 kg) who are virologically suppressed for ≥ 6 months prior to screening. Cohort 2: HIV-1 infected children (6 to \< 12 years of age and screening weight ≥ 25 kg) who are virologically suppressed for ≥ 6 months prior to screening. Cohort 3: HIV-1 infected children (≥ 2 years of age and screening weight of ≥ 14 to \< 25 kg) who are virologically suppressed for ≥ 6 months prior to screening. Cohort 4 Group 1: HIV-1 infected children (≥ 2 years of age and screening weight of ≥ 14 to \< 25 kg) who are virologically suppressed for ≥ 6 months prior to screening and unable to swallow tablets. * Documented plasma HIV-1 ribonucleic acid (RNA) \< 50 copies/mL on a stable regimen (or undetectable HIV-1 RNA level according to the local assay being used if the limit of detection is ≥ 50 copies/mL) for ≥ 6 months preceding the Screening visit. 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 (eg, \< 20 copies/mL), the plasma HIV-1 RNA level cannot exceed 50 copies/mL on two consecutive HIV-1 RNA tests. * Stable antiretroviral regimen of 2 nucleoside reverse transcriptase inhibitors (NRTIs) in combination with a third agent for a minimum of 6 months prior to the screening visit. Individuals undergoing dose modifications to their antiretroviral regimen for growth or who are switching medication formulation(s) are considered to be on a stable antiretroviral regimen. * Estimated glomerular filtration rate (eGFR) ≥ 90 mL/min/1.73 m\^2 according to the Schwartz Formula. * No documented or suspected resistance to emtricitabine (FTC), tenofovir (TFV), or integrase strand transfer inhibitors (INSTIs) including, but not limited to, the reverse transcriptase resistance mutations K65R and M184V/I. Cohort 4 Group 2-4: HIV-1 infected children (≥ 1 month of age and screening weight of ≥ 3 to \< 14 kg) who are treatment naive or on antiretroviral (ARV) treatment for ≥ 1 month prior to screening. * Positive confirmatory HIV test (confirmatory nucleic acid-based testing if \< 18 months of age). * On a stable ARV regimen for ≥ 1 month or treatment naive (Individual is considered treatment naive if ARVs were given for prevention of mother-to-child transmission but not for HIV treatment). * For \< 1 year of age, eGFR ≥ the minimum normal values for age according to the information below using the Schwartz Formula, * 30 mL/min/1.73 m\^2 for age \> 4 weeks to ≤ 95 days. * 39 mL/min/1.73 m\^2 for age ≥ 96 days to ≤ 6 months. * 49 mL/min/1.73 m\^2 for age \> 6 months to \< 12 months. * For ≥ 1 year of age, eGFR ≥ 90 mL/min/1.73 m\^2 using the Schwartz Formula. * No documented or suspected resistance to FTC, TFV, or INSTIs including, but not limited to, the reverse transcriptase resistance mutation K65R. * For individuals \< 14 kg, M184V/I AND HIV-1 RNA \< 50 copies/mL will be allowed. Individuals with HIV-1 RNA \> 50 copies/mL should not have FTC, TFV, or INSTI resistance mutations. * Last dose of nevirapine (NVP) or efavirenz (EFV), if applicable, ≥ 14 days prior to enrollment. Note: Other protocol defined Inclusion/Exclusion criteria may apply.