Considering that last year the US negotiators had to fight to get the ROK to pay $879 million for this year’s upkeep, I don’t expect them to pay $5 billion next year:

South Korea and the United States have agreed to conduct discussions in a “reasonable and fair” way on how to share the cost for the upkeep of American troops here, a foreign ministry official here said Tuesday.
The two sides talked about the upcoming negotiations over Seoul’s share of the cost for the stationing of the 28,500-strong U.S. Forces Korea (USFK) for next year, when U.S. National Security Adviser John Bolton visited Korea last week, the official said.
The local daily JoongAng Ilbo reported that Washington has tentatively decided to request that Seoul pay US$5 billion under a renewed bilateral cost-sharing arrangement for next year, more than a fivefold increase from the previous year.
“When U.S. National Security Adviser John Bolton was visiting Korea on July 23 and 24, South Korea and the U.S. agreed to have consultations over the sharing of the defense cost in a reasonable and fair direction,” the official said on condition of anonymity.
Yonhap
You can read more at the link, but it would have been interesting to see the face of Moon administration officials when John Bolton dropped the $5 billion number.









