Apparently, not only the handset has leaked but also the retail boxes have been shown off online. (themrphone.com)
Second, only handsets with Android 8.0 Oreo or newer out of the box must support Project Treble. (androidauthority.com)
As of now, reports suggest that only the handsets which were enrolled into the Galaxy Beta Program are getting the update, but other users should be receiving the stable build very soon as well. (youmobile.org)