You do not need to have API-specific Models in your component. If you do not provide a Model, the API application will use the Administrator models instead. This is usually what you want to do. There are very few cases where the API application needs a different model to both the Administrator and the Site model.
If you do need to create Models, follow the same conventions as
you'd do for Models in the Administrator part of your application. The
only difference is that the namespace prefix uses
Api instead of
Administrator.