The gsutil command has options to optimize upload/download speed for large files. For example
GSUtil:parallel_composite_upload_threshold=150M
GSUtil:sliced_object_download_max_components=8
see this page for reference.
What is the equivalence in the google.cloud.storage python API? I didn't find the relevant parameters in this document.
In general, does the client API and gsutil have one to one correspondence in terms of functionalities?
I think it's not natively supported.
However (!) if you're willing to decompose files then use threading or multiprocessing, there is a compose method that should help you assemble the parts into one GCS object.
Ironically, gsutil is written in Python but it uses a library gslib to implement parallel uploads. You may be able to use gslib as a template.