What are the support windows for SQL Server 2012 SP3 and SP4 respectively? I am hearing two different rumors. One is that SQL Server 2012 SP3 loses support June 2017. I am also hearing SQL Server 2012 SP4 is due out in June 2017. Is SP4 just a rumor? Or is it true? If true, when does SP4 lose support?
SP4 for 2012 was announced recently and is due out next month.

See Microsoft's Support Lifecycle Policy documentation for end-of-support dates.  According to that document, SQL Server 2012 Service Pack 3 "mainstream support" ends on July 11, 2017.  Extended support for SQL Server 2012, including service pack 4, ends July 12, 2022.