completion-cycle-threshold is a variable defined in `minibuffer.el'.
Its value is

Number of completion candidates below which cycling is used.
Depending on this setting `completion-in-region' may use cycling,
like `minibuffer-force-complete'.
If nil, cycling is never used.
If t, cycling is always used.
If an integer, cycling is used so long as there are not more
completion candidates than this number.

You can customize this variable.

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