I'd encourage you to read TFA, but why bother? The submitter clearly didn't either.

I read it. I also searched the page for the word "Opus" and it didn't appear anywhere. The word "Sonnet" appears, but only once.

There's also "GPT-4.1 or GPT-5", but that's not what my question implied, which was that it's weird to offer Sonnet but not Opus.