CMS-0053-F (finalized March 24, 2026; Federal Register 2026-05676) adopts HIPAA standards for health care claims attachments and electronic signatures. The adopted stack pairs X12N 275/277 (v6020) for the transaction with HL7 C-CDA and the HL7 Attachments IG (2022) for clinical content. Effective May 26, 2026; compliance by May 26, 2028.

If a plan just finished CMS-0057 prior-auth documentation flows, attachments is the same muscle applied to claims: get supporting evidence from the provider to the payer without fax trees. On the FHIR side, CDex-for-PAS style attachment patterns are the cousin to watch — PIE WG activity matters for how the FHIR path evolves beside the X12 baseline.

What ImOnFHIR does with it: second mandate story on the comply track and watch-list. Attachment metadata skeletons can note X12 275 as a future inbound shape; we point don't host licensed X12 specs or CPT. The lab's evidence problem (documents for PAS/DTR) is intentionally the same domain, even when the wire format differs.