We only know of one – Prometheans – and neither Forerunner book has heavily implied different classes of fighting Forerunners. The GI information made it out to be a "new Covenant." I just don't see it.
To me, after re-reading the article, I think we will be fighting über sentinels, ready to protect Requiem.
"We wanted to create a set of enemies that work together in collaborative way, where each one of those enemies builds on and accentuates the abilities of the others. So when you face an individual enemy they offer one challenge, but as you layer those enemies together it changes the experience in important ways and heightens the challenge".
It is also very adaptive, each Sentinel transmitting its combat footage to an unknown intelligence that continually upgrades Onyx Sentinel combat algorithms. As per a Spartan: "We are teaching it how to fight."
The Onyx Sentinels can also merge together for a variety of purposes, such as combining to increase firepower and shield strength, architectural purposes, and forming clusters to protect Onyx. Even a pair of Sentinels is exponentially more dangerous than a lone one, as a pair, unlike individual Sentinels, can activate its shields and fire its energy weapon at the same time.
Onyx Sentinels are also known to have other specific tasks beside combat, much like other types of Sentinels. Because of their modular shape, they can transform into several different types of configurations. For example, they can interlace into oblong-shaped formations, which are used for excavating and earth-moving.
