Starting from 2023-10, the Admin and Storefront GraphQL APIs have made the namespace field optional when creating, updating, or querying Metafields and Metafield Definitions. We have updated all relevant mutations and queries to accommodate this change. When working with Metafields from an App, the default namespace will be the app reserved namespace.
This update does not affect API calls that explicitly specify a namespace. However, it simplifies the process of interacting with namespaces by removing the need to provide a namespace field when the default is suitable. As a result, Apps can now create and query Metafields without the requirement of specifying a namespace.
Learn more in the Admin API and Storefront API documentation for Metafields.