The latest FastMM version is 4.991
Delphi XE8 uses FastMM but which version is that?
The version of FastMM that ships as the built-in Delphi memory manager is a customised version that does not correspond to any version from the official FastMM code base. This customised version is cut down and has significantly reduced functionality.
Embarcadero maintains that customised version, and you can inspect it by examining the file <installdir>\source\rtl\sys\getmem.inc. To the best of my knowledge, the Embarcadero version was forked from the official project some time ago and there is a significant divergence.