I would say that functionally reproducible builds are sort of inherent in the concept of “source”. When builds are “not reproducible” that typically just means they’re not bit-for-bit identical, not that they don’t produce the same output for a given input.

Once neural networks enter the scene, I don't think giving the same output for a given input is possible in the field currently. I believe this is as open as language models can be, and what people mean when they say it's a "fully open source" model.