APIs for what precisely? Using an external program to control and manage the gateway via your own mgmt processes?
You would use the REST interface for that.
The online help has some information about that including sample scripts.
An interface is provided that allows you to administer an appliance without being logged on to its standard user interface. This alternative interface is known as the REST (Representational State Transfer) interface.
Using the REST interface, you can perform different kinds of activities on a particular appliance or on others that are connected to it.
Actions — Shutdown an appliance, restart it, flush the cache, create a configuration backup, and perform several other activities
File handling — Access system, log, and troubleshooting files to perform activities such as downloading, modifying, deleting, and others
List handling — Work with lists and list entries to perform activities such as adding, modifying, deleting, and others