We do not have per_tensor_symmetric tensor in the backend actually since per_tensor_symmetric can be represented by per_tensor_affine tensor, e.g. a torch.per_tensor_symmetric, torch.qint8 tensor with a scale would be the same as a torch.per_tensor_symmetric, torch.qint8 with the same scale and a zero_point of 0. You can use per_tensor_symmetric in observers though.