Vertical Biome Generation in Modder Support Posted June 8, 2020 According to the minecraft wiki in snapshot 19w36a "Biome information now stores Y-coordinates, allowing biomes to be changed based on height. However, this is not yet implemented." It looks like horizontally divided biomes will eventually become a feature. As it stands, there might be a roundabout way of accessing the biome y coordinate with reflection, but that comes with a whole host of issues. Your best bet, until it's implemented completely, is going to be to use a sort of jigsaw structure generation.