|Available in: Developer Edition and sandboxes by default, and All other editions with pilot participation.|
Here’s another reason to try restricted picklists: You can take advantage of them in custom metadata types. Custom metadata types are custom-defined types of application metadata that can be packaged and used along with an app. They save time by letting you define configurations and create reusable app components and features. Picklists on custom metadata types are always restricted, so enable restricted picklists to use custom metadata types.
You define the list of values for a picklist when you create the custom picklist field. However, users can introduce other values by loading them through the API. To enable validation of picklist values against the defined list of values, select Strictly enforce picklist values. This prevents users from adding values through the API.
Only a new custom picklist field can be a restricted picklist. You can’t convert an existing non-restricted picklist to a restricted picklist.