Originally launched with 10 services in 2009, the AWS SDK for .NET has been offered as a single package that includes support for all AWS services. Since that time, the number of supported AWS services has grown to 52, and the size of the SDK has become larger. We began to hear more customer requests for splitting the SDK into smaller per-service modules, and this was our primary motivation to start the Version 3 SDK, which has been in preview since April this year.

Source: Amazon Web Services News