Comment by mtdowling

Smithy has something called event streams that send async datagrams: https://awslabs.github.io/smithy/1.0/spec/core/stream-traits....

This is currently used in Amazon S3, Kinesis, Transcribe, and other services.

Smithy doesn’t have a service registry today. However, models can be vended and shared via Maven. Client codegen was designed explicitly to not require coordinated releases of clients and servers (that’s impossible for AWS SDKs).