The ratio is supposedly about 2/1 in the overall top 4% (gifted) based on Mensa membership.

And the number of women gets even smaller the higher you go.

In my experience female students at educational facilities for the gifted were less than a fifth though.

This might be caused by gifted girls misbehaving less or being less likely to get autism,adhd or other mental issues alongside their intelligence thus not being tested before or during primary school. They might just hide it better or their behavior doesn’t get the same attention, whatever it is it’s certainly influencing the testing and thus whether or not they attend special schooling.