The end cars have a space for wheelchairs, and trains 321-20~321-21 feature bike racks and retractable seating.

The second batch of Class 321000 trains were introduced following the Gyeongui·Jungang Line's eastward extension from Paldang to Guksu station.

The third batch of Class 321000 trains were introduced following the Gyeongui·Jungang Line's eastward extension from Guksu to Yongmun station.

The third batch trains were manufactured and introduced in 2009, few months prior to the opening of the final eastward extension.

All trains were delivered with LCD display monitors on the sides (above the doors), and feature newer exterior LED destination signs that are capable of scrolling.

The front end was modified, and had been the blueprint of all subsequent Korail metro cars for the Seoul Metropolitan Subway from 2009 to 2018.

After refurbishment, gangway doors could be automatically opened by the push of a button.