Back from a science fiction convention. Lots of interesting program, many interesting people, plenty of interesting discussion. Like: Is N K Jemisin's trilogy science fiction or fantasy? I was pretty amazed when I heard this question. I had not considered it could be anything but science fiction. Yes, some characters have powers not explainable by current science, but so what. We'd be left with just a tiny crumb of the huge body of work science fiction is, if we were totally rigorous with that demand. It's (imo) perfectly allowable to have the biological equivalent of handwavium that makes spaceships fly from galaxy to another in a matter of hours.
For some, the telekinetic powers in The Fifth Season place the book in fantasy genre. For me, the divide that separates fantasy and science fiction has little to do with actual science. It's geographical. Or geometrical. Fantasy is a genre of fiction that happens on a flat plane. The plane may have high mountains and deep chasms, but overall, it does not curve into a planet. Once the important 'fantasy map' does not conform to the flat paper page, but would require a sphere to present it accurately, we find ourselves in the science fiction genre, regardless of any seemingly magical powers, elves, curses, dwarves, princesses and prophesies. Fantasy happens in the classic Euclidean universe, in which the Sun circles the flat plane of the world, stars are pretty fairy lights, and things are made of the four elements (or five, or whatever) instead of atoms. There just are no molecules in fantasy. And no galaxy clusters. It's a human-scale universe. Science fiction happens in a non-Euclidean universe which on a fundamental level operates under the same conditions as our world.

Thus is this age-old question settled. Now I will take a nap.