Despite the high prevalence of opioid use disorders (OUD) among people with HIV (PWH), treatment among PWH remains low. Integrating OUD care into HIV care may improve OUD outcomes; however, adoption is limited due to multilevel barriers. RESTORE is a low-threshold substance use disorder (SUD) care program integrated into an outpatient HIV-care clinic that provides training and ongoing support for SUD care adoption by HIV providers. This mixed-methods study explored providers' perspectives on barriers and facilitators to RESTORE implementation and adoption of OUD treatment in HIV care. Repeated cross-sectional surveys were administered pre-RESTORE (2019; N = 42) and post-RESTORE implementation (2021; N = 48). In-depth interviews (N = 18) were completed post-implementation. Chi-square analysis assessed differences between pre- and post-implementation responses. Interviews were analyzed using thematic analysis guided by RE-AIM. Acceptability (Acceptability of Intervention Measure [range 4-20], mean = 16.4) and appropriateness (Intervention Appropriateness Measure, mean = 17.9) were high. Adoption of buprenorphine prescribing was high (29.2% post-implementation vs. 4.8% pre-implementation). Comfort managing OUD increased twofold (21.4% to 45.8%; p = 0.02). Inexperience with buprenorphine initiation and time were barriers to adopting OUD treatment. Ongoing mentoring in OUD care was a facilitator. Future research on the integration of OUD care into HIV care should incorporate task-shifting to increase provider-level support for OUD care.