Java Edition 21w06a

21w06a is the ninth snapshot for Java Edition 1.17, released on February 10, 2021, which adds new cave generation and a new build height limit.

Worlds created prior to this snapshot cannot be loaded and edited in this version without NBT editors, due to there being no upgrade path towards the new height.

World generation

 * Caves
 * Added new noise caves, which come in two types: "spaghetti" and "cheese" caves.
 * Added flooded aquifer caves.
 * The old "carver" cave generation still generates, combining with the new caves.


 * Spaghetti caves
 * Long, narrow caves.
 * Utilize noise generators for generation.
 * Can form cave entrances when they intersect with land.


 * Cheese caves
 * Utilize noise generators for generation.
 * Often form caverns of various sizes.
 * Can form cave entrances when they intersect with land.


 * Aquifers
 * Used to generate bodies of water in new caves.
 * Currently only used below Y=31, meaning any noise caves between the two heights are flooded with water. This will be fixed in a later snapshot.
 * Magma blocks may generate at the bottom of these new water bodies, creating downward bubble columns.
 * Replaces the old underwater cave carvers/canyons.
 * Fish spawn in aquifers if it is under an ocean or river.

Blocks

 * Big Dripleaf
 * Will no longer stop tilting while sneaking on, jumping on, or even jumping off it.
 * Will now tilt quicker.
 * Now tilt when hit with a projectile, instead of being broken.
 * Can now be used with redstone.
 * Powering a dripleaf will now prevent it from tilting down.
 * Powering an already tilted dripleaf will tilt it back up.
 * Powering a dripleaf down will allow it to tilt down again.
 * Powering a dripleaf does not prevent tilting because of projectiles.


 * Hanging Roots
 * Texture has been changed.


 * Small Dripleaf
 * Texture has been changed.

World generation

 * Chunks
 * The Overworld now has a total height of 384 blocks.
 * The world has been extended 64 blocks up and 64 blocks down, which means it's now possible to build from layer -64 to layer 319 in the Overworld.
 * Ore placement below Y=0 is temporary, and underground lava does not generate properly yet.


 * Mineshafts
 * Mineshaft pieces no longer generate if they were fully floating in the air.
 * Corridors now generate with (bark) wood pillars for support if needed.
 * Cobwebs no longer generate floating without an adjacent block.

General

 * World selection menu
 * Disabled the loading of old worlds temporarily.

Video
Video made by slicedlime on the gameplay changes:

Video made by slicedlime on the technical changes:

Trivia

 * This is the first "a" snapshot for the Caves & Cliffs update in which no new items were added.
 * This snapshot marks the first time since 12w07a, almost exactly 9 years prior, that the height limit was increased.