AMD will likely announce its high-end Navi product or products in a fast-approaching future, Q4 we think. On the Chinese Chiphell forum and on the Taiwanese PTT the rumour mill has been cranked up a notch. It seems there are two variants of the alleged Navi 21 GPU.

The news of two versions obviously would not be a surprise as historically AMD always has had a PRO and XT version of their cards. e.g. 5700 and 5700 XT. The chatter now, however, is that one product would get 16 GB GDDR6 memory (which is an awful lot, then again AMD wants to fight NVIDIA's Ampere), the second would have 12 GB of this memory. The news comes from a Chiphell user named 'wjm47196', who, according to Heise, was right with his information about the RX 5600 XT in the past as well.

Then user "AquariusZi" in the Taiwanese PTT forum confirms that AMD is pairing the Navi-21 GPU with GDDR6 and has it manufactured by TSMC in the N7+ process with extreme ultraviolet exposure. 16 GB could be implemented on a 256 or 512-bit wide memory interface. Samsung, among others, offers GDDR6 with 18 GBit/s (4500 MHz), which would come to 576 GByte/s on 256-bit wide memory bus or shockingly 1.15 TByte/s on a 512-bit wide bus. Make no mistake though as 512-bit interfaces are rare as that is a just a daft amount of trace wires in a PCB. For 12 GB, AMD would have to cut the controller to 192 or 384 bits. AMD's Lisa Su confirmed several times that "Big Navi" should appear this year. 

AMD Big Navi would see two product versions with different GDDR6 sizes (12- and 16 GB)