It is possible to access your USS allocation through an S3 API, however, a request must be made for the gateway to be provisioned. The following pages are intended to provide examples for how you might interact with the S3 API either via a graphical user interface, command line interface, or from a python script:
What is the difference between USS S3 and SDSC Cloud Storage?
Please see the FAQ answer on the What is the difference between SDSC Cloud Storage and USS S3? page.