People keep saying this like it means anything besides "you can keep using the adventures we keep in print." Everything else is going to get updated and phased out, with more recent offerings likely having the longest life. But Xanathar's and Tasha's are going to go the way of Volos and Modenkainen's with the first 2024 splat.Given that 2024 is supposed to be backwards compatible, they shouldn't.