Project Summary/Abstract America’s increasing HIV epidemic among youth aged 12-24 and our concurrent failure to identify, link to care, sustain support services and achieve viral suppression among youth living with HIV suggests the need to scale-up and sustain community-based strategies to leverage gateways and settings where high risk and infected youth can be engaged in HIV prevention and treatment. Sexual and gender minority and racial/ethnic minority youth in the U.S. are at disproportionate risk of acquiring HIV due to syndemic factors and low PrEP uptake, yet effective and scalable interventions for youths remain limited. This study will accelerate the implementation of Adolescent HIV Medicine Trials Network (ATN) Protocol 149 Optimizing the HIV Prevention Continuum for Youth intervention package that was developed to be responsive to the needs and preferences of implementers and youth. This study proposes to develop with community partners implementation support strategies to prepare for a hybrid type-2 effectiveness-implementation study to test implementation strategies and validate intervention effectiveness in a real-world replication study. Phase 1 Qualitative Interviews and Networking. Interested parties (stakeholders) from Southern California public health and frontline HIV prevention organizations will be interviewed, including agency leaders (n=10) and frontline prevention workers (n=30). The Consolidated Framework for Implementation Research (CFIR) will guide semi-structured interviews and rapid qualitative data analyses for exploring qualitatively the barriers, facilitators, preferences, and opportunities for implementation of the ATN 149 interventions for two primary strategies: 1) agency staff training and delivery by frontline workers; or 2) direct-to-youth delivery by dedicated program staff with reciprocal agency linkages. Phase 2: Intervention Package Update & Type 2 Hybrid Implementation-Effectiveness Trial Preparation: Phase 1 will inform a plan for updating and adapting the intervention package based on one or both implementation strategies. Implementing partners from Phase 1 will be engaged in collaboratively adapting and updating protocols, training materials, text- message libraries, peer support forum, and the mobile-web intervention management system for text-messaging and coaching implementation support.