The apps API group will be where the v1 Deployment type lives. The apps/v1beta1 version was added in 1.6.0, so if you have a 1.5.x client or server, you should still use the extensions/v1beta1 version.
The apps/v1beta1 and extensions/v1beta1 Deployment types are identical, but when creating via the apps API, some improved defaults are used