This study investigates the role of Open Government APIs (OGAPIs) in enhancing smart city service delivery across five countries with varying digital governance maturity: Singapore, South Korea, the United Kingdom, Brazil, and Indonesia. Employing a comparative qualitative literature review, the research synthesizes findings from academic sources, government publications, and international benchmarks. The analysis is framed around four key dimensions: policy and legal infrastructure, technical and data architecture, organizational readiness, and citizen engagement. Results reveal that countries with centralized digital strategies and standardized API frameworks, particularly Singapore and South Korea, achieve higher integration, transparency, and real-time responsiveness. In contrast, Brazil and Indonesia demonstrate fragmented implementation, hindered by institutional gaps and lack of enforceable legal mandates. The United Kingdom presents a hybrid model balancing decentralization with design standards. The study underscores that the success of OGAPIs is not merely technical but depends on legal enforceability, civic engagement infrastructure, and interagency coordination. Policy implications suggest investing in middleware platforms, adopting binding API standards, and fostering civic tech ecosystems. The findings contribute empirical insights for designing inclusive, efficient, and accountable smart city services through programmable governance interfaces.