US will add extra F-15s to its Air Force inventory. According to a source speaking to Air Force Magazine “the Pentagon’s decision to add new F-15EXs to its budget request for the Air Force, was based on a lack of capability and capacity of the current fleet and the presumptive cheaper cost of the Eagles”, the military’s top uniformed officer told lawmakers on Thursday.

The Pentagon’s fiscal 2020 budget request includes about $1 billion for eight F-15EX “advanced Eagles,” a decision that stemmed from former Defence Secretary Jim Mattis.

According to sources, The F-15EX initially would only be “slightly” cheaper to buy than a new F-35, it will be more than 50 percent cheaper than the Joint Strike Fighter to operate over its life. Additionally, it has “twice as many hours” in terms of how long it lasts.
However The primary aircraft of the future for the Air Force is and will remain the F-35.