dynamic-completion-mode

dynamic-completion-mode is a variable defined in `completion.el'.
Its value is

nil

Documentation:
Non-nil if Dynamic-Completion mode is enabled.
See the command `dynamic-completion-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `dynamic-completion-mode'.

You can customize this variable.