Looks like it was cooperative until OSX actually. I just remembered that it was a loooooong time compared to other desktop OSs.
> With the release of System 7, the MultiFinder extension was integrated with the operating system, and it remains so in Mac OS 8 and Mac OS 9. However, the integration into the OS does nothing to fix MultiFinder's inherent idiosyncrasies and disadvantages.[11] These problems were not overcome in the mainstream Macintosh operating system until the MultiFinder model was abandoned with the move to a modern preemptive multitasking Unix-based OS in Mac OS X.
> With the release of System 7, the MultiFinder extension was integrated with the operating system, and it remains so in Mac OS 8 and Mac OS 9. However, the integration into the OS does nothing to fix MultiFinder's inherent idiosyncrasies and disadvantages.[11] These problems were not overcome in the mainstream Macintosh operating system until the MultiFinder model was abandoned with the move to a modern preemptive multitasking Unix-based OS in Mac OS X.
https://en.wikipedia.org/wiki/MultiFinder