In SuperBPE, a fixed number of tokens are learned, and then the constraints of pretokenization are removed entirely, and then the remainder of the target vocab size is learned.

In Boundless BPE, no schedule must be chosen, because there is not any point at which the constraints of pretokenization are removed entirely. Instead, at any point in the learning process, merges between adjacent pretokens are permitted if the pretokens are each represented by a single token. There are some additional details about how the authors incorporate Picky BPE, which I will not try to repeat because I would probably get them wrong.