The Hybrid Annuity Model (HAM) is an availability-based infrastructure financing framework that combines public funding support with private sector capital participation to improve project bankability and capital efficiency. Under this model, the public authority provides milestone-based construction payments while the concessionaire finances the remaining portion and receives inflation-indexed annuity payments during the operational phase. This structure reduces private capital deployment requirements, improves financial viability, and creates predictable, sovereign-backed cash flows suitable for institutional investment. Financial modeling demonstrates that milestone funding and annuity recovery mechanisms significantly enhance equity efficiency while maintaining stable long-term returns. Inflation indexation protects construction cost exposure, and the ability to monetize annuity-backed assets enables capital recycling. HAM represents a scalable infrastructure financing solution that improves capital allocation efficiency, mobilizes private investment, and supports sustainable infrastructure development, particularly in policy-stable and capital-rich environments such as the Middle East.