The Couchbase .NET SDK 2.1.0 GA release includes several new features such as support for the Task Asynchrony Pattern (async and await keywords) and non-blocking IO for all Key/Value operations, enabling developers to write asynchronous code using the SDK. Additionally, the release introduces new extension points for creating "pluggable" Transcoders, Serializers, and Converters, allowing users to customize their experience with the SDK. Other notable features include per connection TCP KEEP_ALIVE settings, official support for a "key exists" method, and improvements to query-request engines and bug fixes.