From version 1.10.0 onwards GRIB API is released under:

 

Versions of GRIB API prior to 1.10.0 were released under:

Copyright 2005-2012 European Centre for Medium-Range Weather Forecasts (ECMWF)

 Licensed under the GNU Lesser General Public License which
 incorporates the terms and conditions of version 3 of the GNU
 General Public License.                                                                                    
 The texts of these two licenses can be found in

http://www.gnu.org/licenses/lgpl.html

http://www.gnu.org/licenses/gpl-3.0.html