The usage API is available in the Go SDK (Docs)

Access the protos: messages, service request and response

Requires Global Admin or Account Owner privileges to call the usage API

Usage is broken down in terms of Actions and Storage by Namespace by Day; results are returned inline

Note that there is some data processing lag time - the API provides an "incomplete" field to indicate if a day's data is still processing and not yet complete

Official Temporal documentation is coming soon