Early versions of the Hurd were developed on top of CMU's Mach 3.0.
In 1994, CMU stopped working on Mach, and the GNU Project switched to Utah's Mach 4. The kernel known as "GNU Mach" was derived from Mach 4 once Utah stopped development. The first ChangeLog entry by Thomas Bushnell (rather than by a Utah researcher) is from 16 December 1996.
In 2002, Roland McGrath branched the OSKit-Mach branch from GNU Mach 1.2, intending to replace all the device drivers and some of the hardware support with code from OSKit. After the release of GNU Mach 1.3, this branch was intended to become the GNU Mach 2.0 main line; however, as of 2006, OSKit-Mach is not being developed.
GNU Mach 1.4 was released on 27 September 2013, eleven years after 1.3.