How far they went is not known.

Beust has asserted in his correspondence with the French Foreign Minister, the Duc de Gramont (formerly ambassador at Vienna), that they never were more than discussions, and that they ended in 1869 without any written agreement.
The sole understanding was to the effect that the policy of both States should be friendly and pacific, Austria reserving the right to remain neutral if France were compelled to make war.

The two Empires further promised not to make any engagement with a third Power without informing the other.
This statement is not very convincing.

States do not usually bind themselves in the way just described, unless they have some advantageous agreement with the Power which has the first claim on their alliance.

It is noteworthy, however, that the Duc de Gramont, in the correspondence alluded to above, admits that, as Ambassador and as Foreign Minister of France, he never had to claim the support of Austria in the war with Prussia[12].
[12] _Memoirs of Count Beust_, vol.ii.pp.