They essentially have, from what I’ve heard, a middleware model (perhaps 3.5) that serves as an entry point, receiving the prompt, simplifying it, and then sending it to GPT 4.
However, I agree that it is gradually waning. Particularly after the release of the GPTs, both 4 and 3.5 have become incredibly stupid. Complete disregard is given to prior instructions and context. It cannot respond to a basic email, not even when given explicit instructions on what to say. Asking to generate Code is basically useless you won’t get anything usable.