The F-23 Falcata is an atmospheric fighter that served in UNSC Air Force reserve units during the opening years of the Covenant War. Largely supplanted by the S-14 Baselard in UNSC service, surplus Falcata airframes have found a new niche with planetary defense forces who appreciate a capable atmospheric fighter which is relatively economical to maintain and operate from austere airfields.

My best guess is that it was one of the original ideas for what became the Sabre, but we will see how it works in the Digsite mod