http://www.pcgameshardware.de/Grafik...eld-4-1090085/
PCGH asked Raja Koduri about Mantle and its "openess". He replied that AMD doesn't see Mantle as an open standard like OpenCL or OpenGL. He also tried to brush aside comparisons with Glide but then stated: If a competitor were to approach AMD to make their own backend and drivers for Mantle, AMD would not dismiss them right away.
That doesn't sound very open to me. In the letter of the word it may be "open", but in the spirit, this thing is clearly proprietary since AMD has the final say over changes/features and who to admit (and who not) and there is no independent group involved in its inception and ongoing development. This leaves a very sour taste in my mouth, no matter the possible advantages.