When Google announced its Stadia platform, a cloud-based game streaming service similar to GeForce Now, there was plenty of speculation about the hardware. Google has been somewhat vague on what exactly powers Stadia game streaming, such as the CPU (which we can probably assume is a quad-core Xeon), and the GPU that it just described as a custom AMD GPU armed with 56 compute units and HBM2 memory.
The timing of Google's Stadia launch in March left more questions than answers in regard to the graphics behind the service. AMD's first 7nm gaming GPU, the Radeon VII, launched in January, making it possible that AMD already had a large customer for its 7nm products. This, however, doesn't seem to be the case.
Khronos, the organization behind the development of the Vulkan API, recently listed Google's Stadia platform under a list of "conformant products" (GPUs that use Vulkan). The description for Google's GPU reads "Google Games Platform Gen 1 (AMD GCN 1.5)", which tells us that Google is using the 1.5 version of AMD's Graphics Core Next (or GCN) family of graphics architectures.
Every generation, AMD has bumped up the version of GCN from 1.0, to 1.1, to 1.2., and so on. It currently sits at version 1.5.1, which denotes 7nm Vega. However, Google is using GCN 1.5 for Stadia, not 1.5.1.
GCN 1.5 is actually the original Vega architecture that's based on the 14nm process and debuted with the Vega Frontier Edition. In fact, every non-7nm Vega product is GCN 1.5, such as the Vega 56, which many suspected AMD had modified slightly to create Google's custom GPU. Google's GPU has the same 56 compute units as the Vega 56, but it seems AMD bumped up the memory clock speeds to match the Vega 64 (which has 484 GB/s of memory bandwidth).
Google's specifications do mention the Stadia GPU has 16GB of RAM, but considering that it says "up to 484 GB/s" of throughput, it's likely Google means there's 8GB of HBM2 VRAM on the GPU and 8GB of standard DRAM on the motherboard. If this were 16GB of HBM2, we'd likely be seeing almost a TB/s in bandwidth instead.
It would be really cool if Google were using AMD's 7nm Vega, but it seems like Stadia is a good chance for AMD to leverage its investments in an existing, mature, and proven architecture to generate more revenue. As with any platform, Google's Stadia will evolve, meaning AMD's 7nm Navi architecture, which comes to market in Q3, could make an appearance in the future.