gnus-mode-non-string-length

gnus-mode-non-string-length is a variable defined in `gnus.el'.
Its value is

30

Documentation:
*Max length of mode-line non-string contents.
If this is nil, Gnus will take space as is needed, leaving the rest
of the mode line intact.

You can customize this variable.

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