A spy photo underneath the fairing of the 2013 Yamaha M1 2013 is adequate to reveal the twin spar development as well as raise questions about the objectives of the Yamaha engineers. 

2013 Yamaha M1

 The comparison with the 2006 Yamaha M1 that detailed photos had been published, is striking. As it can be seen, the frame is no longer a typical twin spar frame, or Deltabox as Yamaha named it after developing and introducing it at a production bike, the 1987 FZR 1000. Especially at the front section there is a triangle formed, unifying as a part of the frame, the bars at the front of the engine, something that resembles to a monocoque perception at the cylinder head area. 

2006 Yamaha M1 

Additionally the head pipe and the swingarm pivot are connected almost in a straight line, decreasing the vertical frame sections at that point. Probably this is an effort to manage better the forces under braking and mid-corner. Thus one could say that this frame is a tiny Yamaha convergence (maintaining all the proven value of the twin spar frame as this has been evaluated in racing and production bikes) to the non-frame perception by Ducati in the last years of MotoGP racing, which …didnt work though.  
1987 Yamaha FZR1000

Source: gpone.com