To pull this off, we are introducing torch.jit, a just-in-time (JIT) compiler that at runtime takes your PyTorch models and rewrites them to run at production-efficiency. The JIT compiler can also export your model to run in a C++-only runtime based on Caffe2 bits.

In 1.0, your code continues to work as-is, we're not making any big changes to the existing API.

Making your model production-ready is an opt-in annotation, which uses the torch.jit compiler to export your model to a Python-less environment, and improving its performance. Let's walk through the JIT compiler in detail.
torch.jit: A JIT-compiler for your models