[PyQt] Why with PyQt5, The GIL is only released when it is known to be needed ?

[Baptiste de la gorce]

Hello,
I can read on the PyQt5 documentation that "The GIL is only released 
when it is known to be needed. PyQt4 always released the GIL when 
calling Qt." Why this choice to release the GIL less often withPyQt5 
than with PyQt4? I'm developing a software with several threads (one for 
GUI, one with high CPU usage, others for IO). I'm using PyQt4 and wish 
to switch to PyQt5, but am afraid to have something less responsive.

Baptiste.