Python 3.9 is now generally available.

google.appengine.api.modules.set_num_instances_async

Returns a UserRPC to set the number of instances on the module version.

instances The number of instances to set.
module The module to set the number of instances for, if None the current module will be used.
version The version set the number of instances for, if None the current version will be used.

A UserRPC to set the number of instances on the module version.