The only part about it that looks custom is that it's lower spec than what AMD otherwise sells. Stadia's specs per Google: Custom AMD GPU with HBM2 memory and

The only part about it that looks custom is that it's lower spec than what AMD otherwise sells. Stadia's specs per Google: Custom AMD GPU with HBM2 memory and 56 compute units capable of 10.7 teraflops 16 GB of RAM with up to 484 GB/s of performance Radeon MI25's specs: 16GB of HBM2 memory at 484 GB/s with 64 compute units capable of 12.29 TFLOPs 12.29 * (56 / 64) = 10.7. So this is almost certainly just MI25 chips with 1 or 2 bad 'cores'. Aka, the reject pile. From last generation, at that, since the current gen MI50 & MI60 are both 1TB/s HBM2 memory. The multi-gpu part maaaaay be custom using the Instinct's extra interconnects instead of what used to be consumer Crossfire. But multi-gpu in consumer space is almost entirely dead, and nothing seems to suggest any developer would do anything for multi-gpu in this platform, either.