The release notes are correct for SimpleITK, in that it defaults to the new behavior. I believe that there was a discussion some place about why the legacy behavior was wrong it would probably be good to include that in the notes. So you know where the discussion occoured? Is this it: Sobel operator extended for 4D, legacy support for 3D, OK?
SimpleITK has the defaults explicitly specified as UseLegacyOperatorCoefficients=OFF.