From the Summary: "On March 11, 2021, the U.S. Air Force took delivery of its first F-15EX Eagle II fighter. The original Eagle II program was intended to deliver 144 aircraft to replace aging F-15Cs, most of which are in the Air National Guard; however, the FY2023 President's budget request adjusts the intention of procuring 80 aircraft. The Biden Administration's FY2023 budget proposal included a request for $2.6 billion to buy 24 F-15EX aircraft, the second to last procurement toward a planned initial buy of 80. The subsequent FY2022 defense budget proposal requested about $1.32 billion in procurement funding for 12 Eagle IIs and $133.5 million in advance procurement for future aircraft. The proposed budget also requested about $118.1 million for F15EX research and development."
CRS Report for Congress, R46801
Congressional Research Service: https://crsreports.congress.gov/