This just in from the FIM:
FIM Road Racing World Championship Grand Prix Decision of the Grand Prix Commission
The Grand Prix Commission, composed of Messrs. Carmelo Ezpeleta (Dorna, Chairman), Ignacio Verneda (FIM Executive Director, Sport), Herve Poncharal (IRTA) and Takanao Tsubouchi (MSMA) in the presence of Javier Alonso (Dorna) and Mike Trimby (IRTA, Secretary of the meeting), in an electronic meeting held on 22 May 2014, made the following decision:
The Commission unanimously decided, in the interests of safety, to modify the regulation concerning the front carbon disc brake sizes in the MotoGP class.
Currently the regulations permit two sizes of front carbon discs; 320 mm discs must be used at all circuits except at Motegi where the use of 340 mm discs is mandatory and at Montmelo and Sepang where use of 340 mm discs is optional.
Following a recommendation from the Safety Commission and with the support of the brake manufacturers it has been decided that the use of 340 mm disc brakes will be optional for all circuits with the exception of Motegi where such use remains mandatory.