Delta's Gradual 757 Retirement (simpleflying.com)

Delta is retiring its Boeing 757s gradually because no single like-for-like replacement exists, with the timeline also outside the airline's control. As of June 30, Delta had 91 757s (75 -200s and 16 -300s), and it has firm orders for 90 Airbus A321neos and 100 Boeing 737-10s to fill the gap.