If you absolutely cannot wait that long (and how could you?) it’s now available as an electronic advanced reading copy (eARC) directly from Baen Books. Here’s the link to their main site and you’ll see How Dark features as one of the new e-releases this month.
You should check out the Baen site even if you don’t intend to buy the eARC, as the site has the first seven chapters up as a free reading sample. That should help you decide whether the book is to your taste (although really, how could it not be?)