Waht language? Because I'm guessing they work well for languages with a large amount of training data like Python (in my experience), less well for less used languages like Zig or Clojure (haven't tried them but that's my theory)
From my experience, GPT-4 works well with both Clojure and Zig. A lot of it depends on the way you prompt though. For example, asking to start with a C or C++ example and converting to Zig often works better than starting straight with Zig. The same strategy works with Java and Clojure too.
I use it for Rust and it's.... meh. It gets things wrong enough that I don't reach for it except to help me reference certain docs. It tends to hallucinate APIs and semantics that just don't exist. Honestly couldn't imagine using it with a dynamic language.
Python here. And like they said, only noticable in the last few weeks.
I've been seeing this too. Always hard to tell what's a real change vs the rolls of the dice lately but I've been having weird python inconsistencies too, in very short snippets doing pretty simple things.