Phase 3, a northern extension of the line, will extend the line northwest of Gangnam to Yongsan Station. This additional stretch is estimated to cost at least 400 billion won. Because part of the line lies inside the Yongsan Garrison, the phase was split into two sections. One section, an extension from Gangnam to Sinsa, started construction in 2016 and is slated for opening in January 2022. The other section, a further extension from Sinsa to Yongsan, will start construction and will open no earlier than 2027.