The profile of Shternshain specifically mentions the Radeon R9 380X and before the news got picked up by online media Zhang proudly claimed on his profile that he was project manager for world's first "300W 2.5D discrete GPU SoC using stacked die High Bandwidth Memory and silicon interposer".
Zhang doesn't specifically refers to the 380X so it could be that he's talking about a follow-up GPU but the blurbs of text seem to suggest the chip has already been finished. If this is indeed the Radeon R9 380X, it seems we're going to get a 28nm chip with 300W TDP and HBM.
HBM is expected to be the next big thing in the GPU market and all things point to AMD being the first one to adopt this new technology. If it all works out, the initial version of HBM promises at least equivalent bandwidth to the memory found on today's high-end graphics cards, but with significantly better access latency and reduced power consumption.