The US invested $8 billion into upgrades... and then killed off the program due to tons of problems with the upgrades[1]:
> However, the program was unable to deliver needed capabilities on an operationally relevant timeline at an acceptable level of risk to meet the GPS constellation modernization needs.
Hopefully the newer equipment and incremental improvements can bridge over to whatever's next.
Their L5 signal has been in experimental operation for probably over a decade, still "experimental".