The following applies to latest "Development stream", currently based on kernel 4.0.
IBM support is available for
for Linux on z Systems™ running:
The Announcement for the z13 includes a re-branding of 'IBM System z®' to 'IBM z Systems™', which renames 'Linux on System z' to 'Linux on z Systems'.
Linux on System z and Linux on z Systems are used synonymously to refer to Linux running on an IBM mainframe system, including zSeries mainframes in 64- and 31-bit mode.
Starting with the kernel 2.6.27 based 'Development stream', IBM supports only distributions compiled with march=z9-109, so that Linux on z Systems can benefit from the compiler enhancements exploiting z9 instructions.
IBM supports only 64-bit distributions based on this stream; 31-bit applications are supported on the 31-bit emulation layer.