Exchange Server 2016 is here and available to download starting today! We’ve spent nearly three years iterating, polishing and refining Exchange since the release of Exchange 2013, and we are excited to put a shiny, new version of Exchange into your hands today. What sets this version of Exchange apart from the past, is that it was forged in the cloud. This release brings the Exchange bits that already power millions of Office 365 mailboxes to your on-premises environment.
Read more at source: http://blogs.technet.com/b/exchange/archive/2015/10/01/exchange-server-2016-forged-in-the-cloud-now-available-on-premises.aspx