Java Edition 21w43a

21w43a is the seventh snapshot for Java Edition 1.18, released on October 27, 2021, which adds the old world upgrading and fixes bugs.

World generation

 * Old worlds upgrading
 * Terrain from new chunks will now blend with existing terrain from old chunks, preventing glitched borders from occurring.
 * The old bedrock layer between Y=0 and Y=4 in old chunks gets replaced with deepslate.
 * If there is bedrock at Y=0, lower places in old chunks will be filled with deepslate.
 * Caves do not generate below Y=0 in old chunks but lava lakes and geodes may generate.
 * A new bedrock layer is placed at Y=-64.
 * Worlds upgraded in this snapshot have these changes permanently applied.

General

 * Tags
 * Added block tag.

Blocks

 * Big Dripleaf
 * Restricted big dripleaf placement to clay, coarse dirt, dirt, farmland, grass blocks, moss blocks, mycelium, podzol and rooted dirt.

World generation

 * Aquifers
 * Water levels change less often (slightly fewer underground waterfalls).
 * Lava aquifers are slightly less common.


 * Caves
 * Reduced the amount of flooded caves near river and ocean coastlines.


 * Ocean
 * Removed deep warm ocean biomes.
 * Warm ocean biomes now generate in deep waters.


 * Seeds
 * Have been reshuffled again. Worlds will not look like as they did in previous snapshots.

General

 * Chunk format
 * Removed chunk’s  and moved everything it contained up.
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 * Added  the minimum section y position in the chunk.
 * Added  containing data to support below zero generation.
 * Added  containing data to support blending new world generation with existing chunks.


 * Options
 * The Priority Updates video setting has been renamed to Chunk Builder, added tooltips to its three options, and renamed them:
 * "nearby" renamed to "Threaded".
 * "by player" renamed to "Semi Blocking".
 * "none" renamed to "Fully Blocking".


 * Tick
 * Changed some internal details of block and fluid ticking to improve save times.

Video
Video made by slicedlime: