Starting July 1st, Microsoft will be adding SQL Server 2014 to the list of license grants for Team Foundation Server 2013. SQL Server 2014 is supported by TFS 2013 with the caveat that it has increased hardware requirements compared with previous versions.
Microsoft also has a KB Article titled “Performance decreases in TFS 2013 Update 2 after you upgrade to SQL Server 2014” which you should also be aware of if you have a large configuration (> 500 users). It specifically addresses a Work Item Tracking performance issue and can be easily mitigated by increasing the RAM by 410MB on the server hosting the SQL Server instance for each Team Project Collection database.
Example: two (2) Team Project Collections X 0.4 GB = 0.8 GB of RAM
Note: If you have SQL Server Reporting Services deployed on a separate server in your TFS 2013 environment make sure you don’t forget to upgrade it as well.
Another important point regarding SQL Server 2014 support, is if this SQL Server instance is also shared with SharePoint 2013. All updates for SharePoint require the March 2013 Public Update for SharePoint 2013.
It is of course recommended to install the April 2014 Update (includes SP1) followed by the June 2014 CU. The June CU includes a fix for a regression the April CU created related to authentication (claims conversion bug). SQL Server 2014 support for SharePoint 2013 was introduced in the April 2014 CU but due to a regression it is recommended the June 2014 CU be applied.
UPDATE 11-July-2014: Warning: System Center 2012 R2 DOES NOT SUPPORT SQL Server 2014. If you share your TFS 2013 database server with System Center 2012 R2 Virtual Machine Manager (SCVMM) for Lab Management you will have to wait. SCVMM 2012 R2 doesn’t even support SQL Server 2012 SP2 so be extra patient🙂