We've noticed that the time for bulk user updates is variable and sometimes extra slow for a small percentage of users (up to several hours). Is there any good way to update a large number of users with immediate effect?

There is a List Upload for CSV files but as far as I can tell, that is not available in the API.

Or maybe create a Static List with the API and add many users to it, but I am not sure if that handles large amounts of users at once.

In general, does Iterable support or plan to support updating large amounts of users in a quicker way than Bulk update?