There have been hints dropped though every once in awhile by the USAF just to scare small children.
I would say that they have easily popped the Mach 10 barrier and are probably looking to double that
Mack 10 is 6,500MPH+++ that is equal to flying from San Francisco to New York in a blazing 45 minutes or less.
Though my curiousity is great I do agree with Patty that they need to keep it secret in order to keep our tech edge.