The Tessara Payer FHIR Drift Index — Q3 2026

What it measures

Across approximately 200 mid-market US payers (Medicare Advantage + Medicaid Managed Care Organizations), the Tessara Drift Index scores CMS-0057-F + CMS-9115-F endpoint conformance drift from baseline. Methodology runs against public /metadata and CapabilityStatement endpoints only — no PHI, no authentication, no scanning beyond what an audit kit would see. Every score is signed and independently re-verifiable.

Methodology

Full methodology specification at /drift-index/methodology — scaffold; the live spec publishes alongside the Q3 release. The six-category drift taxonomy (Mandatory Element Removal, Type or Cardinality Change, Structural Extension, Auth Deviation, Endpoint Behavioral Change, Spec Version Mismatch) is documented in our FHIR alignment matrix.

Cohort scope

• ~200 plans with more than 50,000 members
• Medicaid Managed Care Organizations + Medicare Advantage
• United States only
• Commercial plans considered for the 2027 edition

Anonymized cohort scoring

The initial release uses anonymized cohort positions — for example, "Top-25 Medicaid MCO, position 14". Named-plan participation is opt-in: any plan can request its anonymized cell be made public under its own attribution.

Pre-notice for ranked plans

Plans appearing in the Index receive a 72-hour pre-notice email before public release. Methodology is shared in advance. Plans may submit corrections or context that will appear with their cell in the published Index.

Open methodology and harness

The drift-detection harness will be released as open source after the patent foreign-filing window completes. Index methodology is published independently and is re-runnable by any third party against the same public FHIR endpoints.

Co-published with

Co-publication proposals are under discussion. Confirmed partners will be announced alongside the Q3 release.