buffer-auto-save-file-format

buffer-auto-save-file-format is a variable defined in `C source code'.
Its value is

t

global value is the same.

• Automatically becomes permanently buffer-local when set.

Documentation:
Format in which to write auto-save files.
Should be a list of symbols naming formats that are defined in `format-alist'.
If it is t, which is the default, auto-save files are written in the
same format as a regular save would use.