The Apeks DS4 is basically a DST without the swiveling turret part. It is therefore a fixed first stage, and this design is well-liked by staunch technical divers around the world. It is also so lightweight, and yet with the dry seal design, it keeps contaminants out of the first stage, and therefore able to be cleaner for a longer period of time. With Apeks being known for their overbalanced DS4, breathing performance is needless to mention.

The Apeks XTX 50-second stage is a compact second stage with an inlet heat exchanger and full metal valve barrel for improved cold transfer efficiency. A Venturi lever allows customised control over the airflow within the housing, directing toward the diaphragm for reduced risk of free-flowing when not in use and toward the mouthpiece for maximum airflow. An inhalation control knob allows the diver to increase the breathing effort required to open the valve if required.

This model is only available in the DIN configuration.