Microsoft has an unreleased Play Store app titled Cortana for Samsung devices available for Samsung devices which have US based Google Play accounts.
While it could be possible that the firm is developing a specialised app for preinstallation on Samsung Android devices–especially with the Microsoft Edition Galaxy S8 on sale now–there is no feature difference between this app and the current one available on Android devices right now.
On the other hand, it has been speculated that Microsoft and Samsung may have done a deal to preinstall a more integrated version of Cortana on Android, Samsung’s phones already ship with Bixby and Google Assistant out of the box both wired in hardware and software respectively.
Even if that were true, It’s hard to imagine what hypothetical gains Microsoft would get out of this, or why a Samsung user would eschew the more integrated personal assistants for a third party one that will invariably be less so.
In any case, you can snag Microsoft’s unreleased Cortana App from the Play Store listing here.