From the FiftyThree announcement:
The FiftyThree SDK lets you take advantage of industry leading features such as palm rejection, advanced touch classification, and effortless Bluetooth pairing.
They’ve thus far announced that Procreate, Noteshelf, and Squiggle are initial SDK partners and I am actually really pumped about this. The Paper app has always been good, but I recently got the Pencil to go with it and it takes the app to the next level. These features, like palm rejection, actually work.
I cannot wait to see this integrated into more apps.