N'weo-pattern Gigas

The Gigas-class fighter-bomber is an older Covenant Elite-manned starfighter. Later it was replaced by the Seraph fighter. It has so far only been mentioned in the description of the Elite Flight Harness armor permutation. Despite the age of this craft, Elite flight harnesses are still equipped to interface with them.

It's possible that this may be the so-called "Covenant Flyer" seen in Halo Wars.