Ask HN: Is it possible to get an option to minimize all comments by default?
i.e.: you would only see the top level comments when you open a post, unless you expend them
However, in the case of a feature directly within the HN interface to collapse all non-top level comments, I think the only option right now would be to write JS to fire click events on the DOM to collapse non-top level comments, and inject it via the console or an extension while on HN.