Decision: Revert to the US Core V5 simple extension, and provide guidance in the extension to use the FHIR R5 gender identity extension instead to allow both multiple Gender Identities and associated dates.  And that this and will eventually be replaced by it in future versions of the FHIR R5-based US Core. Background:   See FHIR- FHIR-37509   and See Changes Here   version 5.0.1 US Core Gender Identity Extension   version 6.0.0-ballot US Core Gender Extension Rationale: This extension is not compatible between v5.0.1 and v6.0.0.  Making a breaking change to a FHIR US Core extension could result in compatibility issues with existing systems, decreased adoption of the specification, reduced confidence in its stability, implementation challenges for developers, and decreased interoperability between systems due to different interpretations of the changes. It is imperative to note that the current extension is a duplication of the FHIR R5 gender identity extension and will eventually be replaced by it in future versions of the FHIR R5-based US Core. In light of this, creating a new extension in US Core would not align with the intended goal of being superseded by the FHIR Core extension.       Please note that we have used OpenAI's chatCPG to assist in answering this question. We review these responses and the information provided is based on our experience and implementer feedback and our design choices for US Core.