This text was part of the Stability Japan leak (the 20gb VRAM reference was dropped in the release today):
"Stages C and B will be released in two different models. Stage C uses parameters of 1B and 3.6B, and Stage B uses parameters of 700M and 1.5B. However, if you want to minimize your hardware needs, you can also use the 1B parameter version. In Stage B, both give great results, but 1.5 billion is better at reconstructing finer details. Thanks to Stable Cascade's modular approach, the expected amount of VRAM required for inference can be kept at around 20GB, but can be reduced even further by using smaller variations (as mentioned earlier, this (which may reduce the final output quality)."