In 2018, the United States Air Force (USAF) and Boeing discussed the F-15X or Advanced F-15, a proposed single-seat variant based on the F-15QA to replace USAF F-15C/Ds. Improvements included the AMBER weapons rack to carry up to 22 air-to-air missiles, infrared search and track, advanced avionics and electronic warfare equipment, AESA radar, and revised structure with a service life of 20,000 hours. Single and two-seat variants were proposed, called F-15CX and F-15EX respectively, with identical capabilities. The USAF opted for the two-seat variant, which can be flown either by a single pilot or by a pilot and WSO for complex missions and, someday, controlling collaborative combat aircraft. One reason for this decision is that only two–seat F-15 models remained in production.

The USAF bought the F-15EX to maintain fleet size as F-22 production ended, the F-35 was delayed, and its F-15Cs aged. Although it is not expected to survive against modern air defenses by 2028, the F-15EX can perform homeland and airbase defense, enforce no-fly zones against limited air defenses, and deploy standoff munitions. In July 2020, the U.S. Defense Department ordered eight F-15EXs over three years for $1.2 billion. In August 2020, the USAF announced plans to replace F-15Cs in the Florida and Oregon Air National Guards with F-15EXs. The F-15EX made its maiden flight on 2 February 2021. The first F-15EX was delivered to the USAF in March 2021, and was flown to Eglin Air Force Base in Florida for further testing.

On 7 April 2021, its official name Eagle II was announced. The FY2021 defense appropriations bill funded F-15EX procurement at $1.23 billion for 12 aircraft, bringing total orders to 20 aircraft. By May 2022, the USAF had ordered 144 F-15EXs. It has proposed reducing its orders to 80. The first operational F-15EXs are not to receive conformal fuel tanks. The Air Force's proposed budget for fiscal 2024 includes funds to buy 24 more F-15EXs, which would bring the planned fleet up to 104 aircraft.
Why is the F-15EX Eagle II an ideal aircraft not an ideal aircraft for conducting modern offensive war fighting?
The Boeing F-15EX Eagle II is not expected to survive against modern air defenses by 2028.  Due to the long time horizon for military hardware acquisition this does not make this aircraft suitable for many offensive war fighting missions over the coming years.