Study to Evaluate the Safety and Efficacy of Lenacapavir (GS-6207) in Combination With an Optimized Background Regimen (OBR) in Heavily Treatment Experienced Participants Living With HIV-1 Infection With Multidrug Resistance

Key Inclusion Criteria: * Adult aged ≥ 18 years (at all sites) or adolescent aged ≥ 12 and weighing ≥ 35 kg (at sites in North America and Dominican Republic) * Currently receiving a stable failing ARV regimen for \> 8 weeks * Have HIV-1 RNA ≥ 400 copies/mL at screening * Have multidrug resistance (resistance to ≥2 agents from ≥3 of the 4 main classes of ARV) * Have no more than 2 fully active ARV remaining from the 4 main classes that can be effectively combined to form a viable regimen * Able and willing to receive an OBR together with lenacapavir * No Hepatitis C virus (HCV) ongoing infection Note: Other protocol defined Inclusion/Exclusion criteria may apply.