You can now include enums in the OpenAPI specification that you use to create an external service. When you add the external service to a Flow action element, the enum appears as a picklist. In other Flow elements and in Apex, the enum appears as its base type. You can use either string or number as the enum value type. Support for enums is only available in external service registrations created after the Summer ’26 release.
Where: This change applies to Lightning Experience and Salesforce Classic (not available in all orgs) in Enterprise, Performance, Unlimited, and Developer editions in API version 67.0 and later.