"superblocks... can either be of size 128×128 or 64×64 pixels" https://en.wikipedia.org/wiki/AV1#Partitioning Unfortunately I don't know of a more authoritative source.

> Unfortunately I don't know of a more authoritative source.

https://aomediacodec.github.io/av1-spec/av1-spec.pdf is the most authoritative source.

"All superblocks within a frame are the same size and are square. The superblocks may be 128x128 luma samples or 64x64 luma samples. A superblock may contain 1 or 2 or 4 mode info blocks, or may be bisected in each direction to create 4 sub-blocks, which may themselves be further subpartitioned, forming the block quadtree."

"use_128x128_superblock, when equal to 1, indicates that superblocks contain 128x128 luma samples. When equal to 0, it indicates that superblocks contain 64x64 luma samples. (The number of contained chroma samples depends on subsampling_x and subsampling_y.)"