Oystehr v1.36 - January 29, 2026

RCM Service

• Eligibility checking endpoint now gives friendly errors or sends a specific data set for various cases where payers have unique requirements.
• Eligibility checking endpoint now writes a CoverageEligibilityResponse resource in the event of a timeout when communicating with the payer.

FHIR Service

• The FHIR API now supports the _summary=true parameter (opens in a new tab). This parameter provides a convenient way to request a reduced set of elements for a resource to minimize payload size.
• Requests that use the _elements parameter (opens in a new tab) now include the SUBSETTED tag in the meta element of returned resources, indicating that the resource is a partial representation.

Zambda Service

• The Node 24 runtime is now supported for Zambda Functions.
• Zambda Functions can now respond with XML content; this is handled seamlessly by the Oystehr TypeScript SDK.

SDK

• FHIR types returned by single-resource FHIR methods (for example, oystehr.fhir.create()) now have types with a known id instead of one with type string | undefined. If you've written type-generic function wrappers for these methods you'll need to perform a short migration.
• The oystehr.fhir.batch and oystehr.fhir.transaction functions now include an unbundle() helper, and oystehr.fhir.batch includes an errors() helper.