There will be 2 versions of the Z4:
First Generation is what we drive: 2003~2008 Z4 Roadsters, Coupe and M. The last Z4 rolled off the Spartanburg, SC plant last week. It is done. No more will be produced in the US.
Second Generation will be built in Germany. The official launch date has not been announced but will be very soon. The BMW Mfg people would not divulge anything more than that.