This world has two genders: Staid (ze/zir) and Vail (ve/vem). They are not assigned based on the baby's genitals, but on the baby's personality through a few simple tests. However, it isn't an ideal culture, as people have to be very gender-conforming and can't easily demand a gender change.
Another interesting aspect is that people have several bodies (3 in average) with only one mind, though Fift has issues with having all zir bodies in the same room. People also have access to the feed, in order to see what happens in other parts of their house or in public places.
This is an excellent gender sci-fi novel, especially for fans of Ann Leckie's works. I can't wait to read more from this author.