AFAIU GIL is still the default, and no-GIL is a build option, you can't select it at runtime.

The big issue is what about all those C extension modules, some of them might require a lot of changes to work properly in a no-GIL world.

> Free-threaded builds of CPython support optionally running with the GIL enabled at runtime using the environment variable `PYTHON_GIL` or the command-line option `-X gil`.

https://docs.python.org/3/howto/free-threading-python.html