allout-abbreviate-flattened-numbering

allout-abbreviate-flattened-numbering is a variable defined in `allout.el'.
Its value is

nil

• This variable is an alias for `allout-flattened-numbering-abbreviation'.
• This variable is obsolete since 24.1;
  use `allout-flattened-numbering-abbreviation' instead.

Documentation:
If non-nil, `allout-flatten-exposed-to-buffer' abbreviates topic
numbers to minimal amount with some context. Otherwise, entire
numbers are always used.

You can customize this variable.