allout-inhibit-auto-fill is a variable defined in `allout.el'.
Its value is

  • Automatically becomes buffer-local when set.

If non-nil, auto-fill will be inhibited in the allout buffers.

You can customize this setting to set it for all allout buffers, or set it
in individual buffers if you want to inhibit auto-fill only in particular
buffers. (You could use a function on `allout-mode-hook' to inhibit
auto-fill according, eg, to the major mode.)

If you don't set this and auto-fill-mode is enabled, allout will use the
value that `normal-auto-fill-function', if any, when allout mode starts, or
else allout's special hanging-indent maintaining auto-fill function,

You can customize this variable.