Is the firing pin on stengun fixed or retractable?

The Sten was a blowback-operated submachine gun firing from an open bolt with a fixed firing pin on the face of the bolt. This means the bolt remains to the rear when the weapon is cocked, and on pulling the trigger the bolt flies forward under spring pressure, stripping the round from the magazine, chambering it and firing the weapon all in the same movement.

However, the current day semi auto version of the Sten has a different operating system, and does use a movable firing pin.