Comment by bigDinosaur

SM is claiming that the latest versions of the SM algorithm (namely SM-19) are vastly superior to FSRS (maybe it is?).

They state in contrast:

We do not dismiss the work behind FSRS. It is a commendable open-source effort and a marked improvement over ancient algorithms like SM-2.

For context, Anki uses SM-2's algorithm (albeit apparently heavily modified for various special cases) if FSRS is not enabled.