The GFS Spring 2016 upgrade was completed today as of 12Z. This was the long awaited upgrade that included the 4DVar inclusion.
For more details on the all the changes to the GFS model see the NCEP technical attachment. In short there should be some improvement in the model performance, but overall there will not be a significant leap in model accuracy with this one upgrade.
http://www.nws.noaa.gov/os/notification/tin16-11gfs_gdasaaa.htm
