The version 8.19 preview is described as such: This release backports all improvements of the 9.0 client to the 8.x major version of the client.
I've noticed some changes that hasn't been backported:

1. GetAliasResponse has a Values property (8.19) instead of an Aliases property (9.0).
2. GetMappingResponse has a Values property (8.19) instead of an Mappings property (9.0).

I guess there are also other response types with the same "issue".