Comment by craigacp

Some of the gradients are present in the TF C API (and thus the C++ API), but it's hit & miss which are in C and which are in Python. There was an attempt years ago to port more gradients to C, but this petered out in the way that most TF related efforts seem to do at Google.

We use the C API to generate gradients for TF-Java, and have some success training models with it. Replicating the Python bits in another language is a huge effort though that we haven't completed.