Fast question here: If I want to start writing my own annotation-processing with Kapt, should I use Kapt2 or Kapt3?

4 :troll:

You write annotation processor without kapt, but using jsr269 API and your AP will work with Kapt, standard Java apt or any other jsr269 implementation (kapt actually uses APT under the hood, just generate java stubs for it) Also "Kapt2" was just some sort transition version from kapt1 to kapt2, 1 and 3 worked in a different way Actually you shouldn't worry about it, everyone uses kapt3 and it's the only supported version, so you can test your AP with Kapt and APT (if you want to support also Java)