“Under the hood, we use an HTTP client built on top of Netty to make the non- blocking HTTP call” “first class support for non-blocking I/O in our async clients” source: AWS Developer Blog
“To provide SDK support for the many services that AWS owns, the AWS SDKs make extensive use of code generation” Code generation https://aws.amazon.com/blogs/developer/aws-sdk-for-java-2-x-released/