Introduction: HL7 Fast Healthcare Interoperability Resources (FHIR) has emerged as a leading global standard for health information exchange and is increasingly central to national digital health architecture and to interoperability across the wider health ecosystem. In India, FHIR underpins key national digital health programmes, including the Ayushman Bharat Digital Mission (ABDM) and the National Health Claims Exchange (NHCX). However, the practical, ecosystem-wide adoption of FHIR beyond national programme requirements has not been systematically assessed.Methods: We conducted a mixed-methods landscape assessment between September and October 2025. Data sources included a structured online survey of ecosystem participants (n=22) representing health information system vendors, hospitals, insurers, third-party administrators, diagnostic laboratories, start-ups, government digital health teams, and academic institutions; ten semi-structured key informant interviews with stakeholders (n=10) engaged in ABDM- or FHIR-related implementation; desk research covering ABDM, NHCX, NRCeS implementation guides, global HL7 resources, and international FHIR practice; and structured field validation with early implementers. Findings were analysed descriptively and thematically, triangulated across data sources, and interpreted against selected international FHIR ecosystems, including the United States, United Kingdom, Australia, Singapore, and Israel.Results: India has established a mandate-driven national foundation for FHIR-aligned health information exchange through ABDM and NHCX, including national implementation guides based on FHIR R4, sandbox environments, and a growing ecosystem of ABDM-certified vendors. However, adoption across the wider ecosystem remains uneven and largely compliance-driven. Most participating organisations self-positioned at exploration or limited-pilot stages, while national programmes and a small number of larger vendors reported sustained operational use. Lack of funding or business incentives appeared among the top three adoption barriers for nearly two-thirds of survey respondents. Twenty-one barriers were identified across institutional, technical, and operational domains, including weak incentives, fragmented and rigid governance, limited validator and tooling infrastructure, terminology gaps, workforce constraints, and confusion between ABDM compliance and broader FHIR conformance.Conclusion: India has moved beyond formal standards adoption in selected national programmes, but ecosystem-wide implementation remains at an early stage. The central challenge is ecosystem-wide adoption — moving beyond compliance within national programmes so that implementers can validate, trust, and use FHIR as shared infrastructure (i.e., institutionalising it beyond mandate). Priorities include participatory governance, a layered, openly governed IG model — with the India Core as a recommended (not mandated) baseline, complemented by domain and programme/network layers, public validator and sandbox infrastructure, terminology services, procurement and reimbursement incentives, focused high-value public-sector use cases, and sustained workforce development. India’s experience offers lessons for other large, federated, and resource-diverse health systems seeking to scale standards-based interoperability.