Just to preempt most of the usual snarky comments -- What's confidential is the contents of the filing, not the fact. All the initial S-1 filings I'm aware of are confidential. After amendments (S-1A filings), the resulting document can be made public. At this time, any details of offering are still volatile, and there's no reason to force companies to publish that information until the final offering details are sol…
EDIT: ohh, that changed in 2017. Now all companies can file confidentially.