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.

General

 * Old worlds upgrading
 * When generating close to old chunks hew terrain is adjusted to better match the existing terrain at the borders.
 * The old bedrock layer between Y=0 and Y=4 in old chunks gets replaced with deepslate.
 * Places lower than Y=0 will be filled with deepslate.
 * A new bedrock layer is placed at Y=-64.
 * Worlds upgraded in this snapshot will have these changes permanently.

Blocks

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

World generation

 * Aquifers
 * Reduced the amount of flooded caves near river and ocean coastlines.
 * Water levels change less often (slightly fewer underground waterfalls).
 * Lava aquifers are slightly less common.

General

 * Chunk format
 * Removed chunk’s  and moved everything it contained up.
 * Chunk’s  has moved to.
 * Chunk’s  has moved to.
 * Chunk’s  and   have moved to.
 * Chunk’s  and   have moved to.
 * Chunk’s  has moved to.
 * Chunk’s  has moved to.
 * Chunk’s  has moved to.
 * Chunk’s  and   have moved to a container structure in.
 * Chunk’s  are now paletted and live in a similar container structure in.
 * 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.


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