From a press release:
Transcend, a world leader in storage and multimedia products, is proud to announce its 16GB and 32GB Registered DDR3 DIMM (RDIMM) modules, designed to maximize memory on Apple's Mac Pro systems from 2013. With four slots of memory available, Transcend's latest high-performance DDR RDIMMs can power the Intel Xeon E3 6-core 3.5GHz, 8-core 3GHz and 12-core 2.7GHz Mac Pro models to a total of 64GB , 96GB and up to 128GB of memory capacity.
It is quite normal to see third-party companies offering solutions that double the maximum capacity announced by Apple for their Macs. Who took the lead with the new Mac Pro was Transcend, which has not yet revealed prices but has already announced 32GB combs 100% tested and with limited lifetime guarantee that will bring the total of the new machines to 128GB. Barbarity! (MacRumors)
Update · 03/18/2014 s 10:20
THE Transcend updated its official statement with values. The 128GB kit for the Mac Pro will cost the trifle of $ 2,480, almost $ 6,000.
Update II · 03/26/2014 s 14:20
It took a while, but the OWC now it also announced its 128GB kit for the Mac Pro and it will cost a little less than Transcend's $ 2,130.