IntroductionIn Viet Nam, key populations (KPs) face barriers accessing HIV services. Virtual platforms can be leveraged to increase access for KPs, including for HIV self‐testing (HIVST). This study compares reach and effectiveness of a web‐based HIVST intervention from pilot to scale‐up in Viet Nam.MethodsA mixed‐methods explanatory sequential design used cross‐sectional and thematic analysis. The pilot launched in Can Tho in November 2020, followed by Hanoi and Nghe An in April 2021. Scale‐up included Can Tho and Nghe An, with 21 novel provinces from April to December 2022.After risk assessment, participants registered on the website, receiving HIVST (OraQuick®) by courier, peer educator or self‐pick‐up. Test result reporting and completing satisfaction surveys were encouraged.Intervention reach was measured through numbers accessing the testing, disaggregated by demographics, and proportion of individuals reporting self‐testing post‐registration. Effectiveness was measured through numbers reporting self‐test results, testing positive and linking to care, and testing negative and using HIVST to manage pre‐exposure prophylaxis (PrEP) use. Thematic content analysis of free‐text responses from the satisfaction survey synthesized quantitative outcomes.ResultsIn total, 17,589 participants registered on the HIVST website; 11,332 individuals ordered 13,334 tests. Participants were generally young, aged <25 years (4309/11,332, 38.0%), male (9418/11,332, 83.1%) and men who have sex with men (6437/11,332, 56.8%). Nearly half were first‐time testers (5069/11,332, 44.9%). Scale‐up participants were two times more likely to be assigned female at birth (scale‐up; 1595/8436, 18.9% compared to pilot; 392/3727, 10.5%, p < 0.001). Fewer test results were reported in scale‐up compared with pilot (pilot: 3129/4140, 75.6%, scale‐up: 5811/9194, 63.2%, p < 0.001).6.3% of all tests were reactive (pilot: 176/3129, 5.6% reactive compared to scale‐up: 385/5811, 6.6% reactive, p = 0.063); of which most linked to care (509/522, 97.5%). One‐fifth of participants with a negative test initiated or continued PrEP (pilot; 19.8%, scale‐up; 18.5%, p = 0.124). Thematic analysis suggested that community delivery models increased programmatic reach. Live chat may also be a suitable proxy for staff support to increase result reporting.ConclusionsWeb‐based self‐testing in Viet Nam reached people at elevated risk of HIV, facilitating uptake of anti‐retroviral treatment and direct linkage to PrEP initiations. Further innovations such as the use of social‐network testing services and incorporating features powered by artificial intelligence could increase the effectiveness and efficiency of the approach.