My experience with output styles for long-running sessions is that Claude starts to forget the terse output style by the middle of the context window. Obviously I don't know if 5.1 suffers the same fate but I ran into this issue with both Opus and Fable 5

That sentence is fine; it’s tolerably annoying. As a long-time HN reader, HN is full of this kind of performative erudition and I’m already used to it. Fable probably learned from the worst parts of HN.