archive-7z-extract is a variable defined in `arc-mode.el'.
Its value is
("7z" "x" "-so")

Program and its options to run in order to extract a 7z file member.
Extraction should happen to standard output. Archive and member name will
be added.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.