[zo7]

They don't seem to explicitly say it, but it might be using the same core code given the structure of the framework and their mentioning that it's a mature codebase several years old. The license file also goes back to NYU before being taken over by Facebook, similar to Torch.

[apaszke]

The core libraries are the same as in Lua torch, but the interface is redesigned and new.

[pavanky]

They are sharing the code base using git-subtrees. So the C and CUDA parts of the codebase will be kept in sync. The modules written in lua or python will diverge.