If you are interested in beta features ahead of the latest GA, you may
opt-in to the v1.1 beta, which is spelled v1beta1. In order to do this,
you will want to import from google.cloud.texttospeech_v1beta1 in lieu of
google.cloud.texttospeech.
An API and type reference is provided for the v1.1 beta also:
NOTE: The client for the beta API is provided on a provisional basis. The API
surface is subject to change, and it is possible that this client will be
deprecated or removed after its features become GA.