Caves & Cliffs Update
Caves & Cliffs is an upcoming major themed update set to release in mid-2021 as Java Edition 1.17 and Bedrock Edition 1.17.0. It was announced in Minecraft Live 2020 and includes new features for caves and mountains.
This update's development on Java Edition started with snapshot 20w45a, which was released on November 4, 2020.
This update's development on Bedrock Edition started with beta 188.8.131.52, which was released on October 28, 2020, although most of the features are behind experimental gameplay toggle until 1.17.0 and wasn't included in the full 1.16.200 release.