bibtex-autokey-names

bibtex-autokey-names is a variable defined in `bibtex.el'.
Its value is

1

Documentation:
Number of names to use for the automatically generated reference key.
Possibly more names are used according to `bibtex-autokey-names-stretch'.
If this variable is nil, all names are used.
See `bibtex-generate-autokey' for details.

You can customize this variable.