California sits at the intersection of healthcare and technology innovation, and the shift toward FHIR-based health data interoperability is accelerating this intersection. California health systems, digital health companies, health plans, and life sciences organizations are all building FHIR R4 APIs and applications — driven by the ONC 21st Century Cures Act Final Rule, CMS interoperability rules, and a broader market demand for healthcare data portability and clinical decision support.\n\nZerosums Technology provides FHIR R4 development services for California healthcare organizations and health technology companies. Our FHIR engineers are experienced with the HL7 FHIR R4 specification, SMART on FHIR authorization framework, US Core Implementation Guide, Da Vinci Project implementation guides, and the California-specific interoperability context including CHHS data exchange initiatives and Cal INDEX.\n\nFor California covered entities and health plans subject to the CMS Interoperability and Patient Access Final Rule, we develop the required Patient Access APIs (FHIR R4 using the USCDI data set), Provider Directory APIs, Drug Formulary APIs, and Prior Authorization APIs. We help organizations understand their compliance obligations, design compliant API architectures, implement required FHIR resources, and configure SMART on FHIR authorization to meet CMS security requirements.\n\nFor California health technology companies building FHIR-based applications — clinical decision support tools, care coordination platforms, population health analytics, patient engagement apps — we provide end-to-end FHIR development services including API design, FHIR resource modeling, integration with EHR FHIR endpoints via Epic MyChart API or Cerner FHIR APIs, and backend FHIR server development. California's health tech ecosystem is the most innovative in the world, and Zerosums helps California companies build the FHIR infrastructure that enables it.