6 trains will be added to Seoul Metro Line 9
5本車両増備で6往復増発へ！ ソウルメトロ9号線ダイヤ改正(2023年12月30日) 서울 지하철 9호선 열차운행계획 변경 알림
https://www.train-times.net/article/seoul20231230
To reduce crowd on Line 9 train, Seoul Metro decided to add 3 Express trains and 3 Local trains, which means that minimum train interval will be shortened from 7 minutes 20 seconds to 6 minutes 50 seconds for each of Express and Local.
I guess more crowd will be estimated after begining through service to Incheon International Airport.
