It is out!

Forward weight design, similar to what you see with some other popular manufacturers.  Head is 450cc.  It will reduce spin compared to the D3.  Keep in mind, when the weight moves forward, the MOI goes down (i.e. it's less forgiving).  Get fit on a launch monitor to find the ideal head design for you.

Jonathan is spot on with his comments.  I demoed the D4 last week at one of the Titleist regional fitting centers.  I was recently fitted for the D3 and wanted to make a comparsion before buying.  I was hoping for some positive improvements over the D3 however, the D4 just came it short for me.  The D4 was less forgiving...it did improve my launch angle by 1 degree but, it did not reduce spin or give me any additional distance.  I'm a 10 handicap and was fitted with the silver rogue 60 stiff , D3 9.5. We even tried several other shafts but,  did not see any improvements other than reducing my launch angle.  Also, the fitting was done with my current ball in play, Pro Vx., and spent 1 hour working with both the D4 and D3.  Just my personal results....be sure to get a fitting before buying.