They will be implicit, i.e. no you wont get all the C2 operators exposed in the torch.* namespace, but where PyTorch operators have equivalent Caffe2 operators, the backends will be merged to just use the Caffe2 kernel instead if it’s more efficient.
Answered in 1. And as of last week, C2 and PyTorch have the same Tensor format (c10::TensorImpl I think)
Not in the long term, yes in the short term
No