In sub-Saharan Africa, retention of HIV-infection people in antiretroviral therapy (ART) is an increasing challenge. However, few mobile health innovations have been tested or proven effective in real-world settings with severe human and financial resource constraints. mHealth innovations that successfully retain more patients on ART, at lower cost, within large-volume public ART clinics in SSA are urgently needed. Lighthouse Trust (LT), the largest public provider of ART in Malawi, operates two large clinics in Lilongwe (Lighthouse (LH) and Martin Preuss Clinic (MPC)) with the Malawi Ministry of Health (MoH) with a combined 35,000 ART patients. 12-month retention at Lighthouse is 72%, below the 90% global target for epidemic control. Both clinics employ a real-time electronic medical records system (EMRS) and implement a resource-intensive patient retention program, Back to Care (B2C). B2C aims to trace patients who miss ART visits by >14 days. LT has over 7800 monthly ART visits, and more than 10% of clients are B2C-eligible. B2C demand, coupled with healthcare worker constraints, results in tracing of only 33% of target clients. Moreover, poor data quality reduces B2C effectiveness. Therefore, LT and the University of Washington’s International Training and Education Center for Health (I-TECH), with support from MoH and Medic, implemented an innovative, proactive, patient retention system using two-way texting (2wT) between new ART patients and staff (1R21TW011658-01). 2wT aimed to resolve potential retention issues before they occur and improve data quality (e.g. identifying transfers), reducing B2C workload. 2wT participants had higher retention estimates (95%, 95% CI 91-975) at 3 months post ART initiation compared to non 2wT patients (86%, 95% CI 82-89%). Preliminary results on retention improvements and workload reduction from R21 phase at MPC were welcomed by MoH. In support of widespread adoption and scale up, MoH requests rigorous evidence from a 2wT randomized control trial (RCT). In R33 year 1, the proposed mHealth study supplement will conduct an RCT at LH and MPC clinics, using the established 2wT system and the existing 2wT operations team, minimizing costs while maximizing evidence generation. RCT compares outcomes among 410 new ART patients randomized 1:1 into 2wT (intervention) and control (standard B2C). RCT outcomes reflect shortened timeline (6- vs. 12-months), but same outcomes: retention (ART outcomes, visit adherence) and B2C referrals. In parallel, parent R33 quasi-experimental, pre-post design (R33 TW011658) will focus on 2wT/EMRs interoperability (Y3) and 2wT enrollments at MPC (Year 3) before expanding to LH (Year 3-4). RCT will contribute to R33 enrollments and generate rigorous evidence in response to MoH requests without changing the proven 2wT intervention or the R33 timeline. This small supplement brings large gains in evidence generation and strengthened MoH partnership. .