I am an ESL speaker but I don't see why the sentence fragment in parentheses couldn't be parsed as relating only to "Python stack" as opposed to "systems not using the Python stack". I read it that way, but again, as an ESL speaker, I might be missing intuition or actual grammatical knowledge that would tick off a native speaker such as, presumably, yourself.

It is based upon context, you are correct that it is ambiguious, as is the problem of most natural language.

-I believe that <inference systems not using the Python stack> (which I do not appreciate) are a way to free open models usage and make AI more accessible.

This reading of the text would lead one to believe they don't appreciate inferences systems not written in python. Given the inference system produced by the author is also not using the python stack (it is in C), we can assume this is not the correct reading.

-I believe that inference systems not using the <Python stack> (which I do not appreciate) are a way to free open models usage and make AI more accessible.

This reading says that the author does not like the python stack for inference, which given the author has produced this inference in C, would support the statement.

That is we have to take both readings and think which one fits the context around it, hopefully this helps :)