The eastern European and central Asian (EECA) region has the fastest growing HIV epidemic globally. We aimed to identify how HIV resources could be allocated for maximum health impact. Between Aug 1 and Dec 23, 2022, allocative efficiency analyses were undertaken for 12 countries in the EECA region (Albania, Armenia, Azerbaijan, Belarus, Georgia, Kazakhstan, Kosovo, Kyrgyzstan, Moldova, Serbia, Tajikistan, and Uzbekistan) using HIV epidemic models developed with Optima HIV. Country models were calibrated to demographic, epidemiological, and programmatic data and validated by national teams. Three scenarios were projected from 2023 to 2030: status quo (continued 2021 spending on HIV programmes); optimised allocation of different spending envelopes to minimise HIV infections and deaths; and achieving 95-95-95 UNAIDS targets by 2030. Aggregated across the 12 models, HIV infections attributable to sexual transmission were estimated to surpass those attributable to transmission through injecting drugs in 2018, with male-to-male sexual transmission accounting for a continuously increasing share. In the status quo scenario, there were an estimated 111 520 (95% CI 28 960-208 270) new HIV infections and 34 530 (17 280-57 410) HIV-related deaths between 2023 and 2030. Aggregated optimisation results suggest that 35 860 (32%) of 111 520 new HIV infections and 9170 (27%) of 34 530 HIV-related deaths could be averted from 2023 to 2030 compared with the status quo, by prioritising antiretroviral therapy and targeted key population programmes. For ten countries, achieving 95% diagnosis was projected to not be possible with the current budget envelope, and for seven countries, this target could require more than three times the current spending. Compared with the status quo, achieving 95-95-95, or as close as possible, could avert 70 880 (64%) of 111 520 new HIV infections and 18 890 (55%) of 34 530 HIV-related deaths from 2023 to 2030. Targeted key population programmes should remain high priorities in the EECA region. Achieving 95-95-95 will require more emphasis on implementing appropriate modes of service delivery that reduce the gap in diagnosis and treatment coverage for people living with HIV. The Global Fund to Fight AIDS, Tuberculosis and Malaria. For the Russian translation of the summary see Supplementary Materials section.