https://sputniknews.com/military/201709261057691172-pentagon-considering-retiring-f35-early/
The US Department of Defense is considering a change in direction with their fleet of F-35s, in which more than 100 fighters would be retired from combat rather than upgraded with a new software configuration.
Of the 1,763 F-35s intended to enter service with the US Air Force, 108 are in need of a software upgrade from Block 2B platform to the combat-ready Block 3F. This configuration change would be time-consuming and expensive, with 150 modifications needed in every aircraft to bring them up to standards.