Am I correct in guessing that the high quality text-to-speech (TTS) is limited to the message reader application for licensing reasons?

There are a number of very high quality voices available from
but those seem to be inaccessible from C++ and thus Python

I'm kind of hoping that I just haven't found the docs, but in case not:

Is the API accessible to third party developers through a commercial license?

Is it forbidden to reverse engineer the API used by the message reader?