Creates the Human Services Workforce Sustainability Act. Requires the Departments of Human Services, Children and Family Services, Juvenile Justice, and Public Health, and other specified State agencies, to complete, by June 30, 2027, a look-back calculation for each contracted human services organization that compares the funding amount awarded to the human services organization in State fiscal years 2026 and 2021 in order to identify the percentage change in funding, if any, to the human services organization between those fiscal years. Provides that based on the look-back calculations, each State agency shall identify the total aggregate amount of additional appropriations needed to ensure that grant amounts awarded by the State agency in State Fiscal Year 2028 are at least 25% more than the grant amounts awarded to grantees in State Fiscal Year 2021. Contains provisions concerning implementation of increased grant funding, subject to appropriation; additional percentage increases in grants amounts beginning in State Fiscal Year 2029; expenditure and certification requirements on contracted human services organizations that receive increased grant funding; oversight by the Department of Central Management Services; the adoption of administrative rules; and other matters. Effective July 1, 2026.