There are companies like IOHK or Mercury that hired large swathes (50?) of Haskell programmers in relatively short time, so I don't think bus factor of the programmer market is an issue. Of course it's still an issue if a company hires 1 or 2 Haskell devs only, and those depart.

> from the past three years [..] the latest I’ve seen were Opus-4.6 and GPT-5.5 struggle a lot with standard GHC Haskell

If your experience is from years ago, I totally get that. For my standards, LLMs were pretty bad before 2026.

I haven't tried any serious LLM Haskell before 2026-02, because it was just not a timesaver.

I had good experiences with Opus-4.6 already on Haskell, such as it having detail knowledge on async exceptions, allowing it to immediately pinpoint difficult bugs that me and other experts missed, e.g. https://github.com/snoyberg/conduit/pull/530

But most of my experience is from Opus >= 4.8. I found it excellent at writing difficult TemplateHaskell and Generics implementations, such as oneshotting Postgres JsonPath queries derived from lens-like field accessors on Haskell types.

Note it's still not great at writing general high-quality "engineering" stuff, e.g. Opus 5.0 writes functions that refer to things out of their scope, such as:

    requireFooOr400 :: MyMonad m => Maybe Foo -> m Foo
    requireFooOr400 x = case x of
      Nothing -> throwHttp400 "Cannot perform [very specific action from the caller]: the inputs have no foo"
      Just foo -> return foo

However, that's not a lack of Haskell understanding, and it does that for all languages, e.g. in Python it keeps writing implementation details into API docstrings instead of function body comments.