Microsoft today started delivering Office 2013 Service Pack 1 as well as SP1 releases for the on-premises versions of Exchange 2013 and SharePoint 2013



From Supersite for Windows:

Office 2013 SP1 improves compatibility with Windows 8.1, Internet Explorer 11 and modern hardware, such as high-DPI devices and precision touchpads. It also provides new apps for Office capabilities and APIs for third-party developers. In addition, Office 2013 SP1 includes all of the monthly security updates that were released through January 2014, and all the Cumulative Updates that were released through December 2013. It also includes all of the previously unreleased fixes that include general product fixes, as well as improvements in stability, performance, and security.

Additionally, SkyDrive Pro has been rebranded as OneDrive for Business, as you'd expect.

  Microsoft Starts Rolling Out Office 2013 SP1