To my knowledge, PyTorch’s mixed precision support (Automatic Mixed Precision package - torch.cuda.amp — PyTorch 1.8.1 documentation 11) does not handle fp8 either.
For 8 bit precision you’d need to look towards quantization to integers or fake quants but that doesn’t really fall under the umbrella of mixed precision, though I’m not sure if that’s core to your request or just ancillary.
For info about quantization, you can see this: Quantization — PyTorch 1.8.1 documentation 24