Exchange Server 2013 Service Pack 1 (SP1) is now available for download! Please make sure to read the release notes before installing SP1. The final build number for Exchange Server 2013 SP1 is 15.00.0847.032.

More details here http://blogs.technet.com/b/exchange/archive/2014/02/25/exchange-server-2013-service-pack-1-available.aspx