[2022] Mistlands compatibility with the older worlds?

Originally posted by Fluffy: So I've started playing two weeks ago maybe, spent ~200 hrs and completed the game in it's current state and i really love my world and what i have built and achieved in it. When the Mistlands is released, will i have to create a new world for the ML content to appear?

Mistlands is fully compatible will older worlds.
You will not have to make a new one =)