I primarily use Opus for a Lisp-like DSL codebase (non public, closed source) and it genuinely has _never_ hallucinated. All it pulls from is BNF, language spec + examples. So I have no idea how people are getting it to hallucinate on _popular_ languages.

I think you forget that they really are stochastic (I'd wager it has hallucinated things to you that wasn't important so you missed it, or you've just been very lucky), and the people you're arguing with are forgetting that there is significant difference in when and how often even frontier LLMs hallucinate. I catch claude every now and then, but isn't the measured hallucination rates down in low single digit percent for claude now?

They said that they hadn't "suffered" from hallucinations in months due to effort they put into harness engineering. It's not quite the same thing as saying hallucinations are never happening for them.

I find hallucinations happen for us with those models, but we've worked on baking in guardrails and fact checking against sources of truth, so that it's less of a problem.

We're engineers. We just try to engineer out the failure modes.