Minecraft: Java Edition Snapshot 21w43a introduces world blending for 'Caves and Cliffs Update'

Minecraft Caves and Cliffs Update Image
Minecraft Caves and Cliffs Update Image (Image credit: Mojang Studios)

What you need to know

  • Mojang Studios is in the final stages of finishing up 1.18 'Caves and Cliffs Update' Part Two for Minecraft.
  • Today, a new Minecraft: Java Edition snapshot is rolling out with new bug fixes and changes, and one significant update.
  • The previously touted world blending feature is included in Minecraft: Java Edition Snapshot 21w43a.
  • The feature aims to blend old worlds with new world generation features, including adding new caves and more below existing chunks.

Releasing alongside a new Minecraft: Bedrock Edition beta, Mojang Studios is in the process of rolling out Minecraft: Java Edition Snapshot 21w43a to all interested PC players, which includes the typical polish and bug fixes we expect this late into development of 1.18 Caves and Cliffs Update Part Two.

There is one interesting new development here, however, as Mojang is now introducing the world blending feature first talked about during Minecraft Live 2021. This innovative addition to Minecraft makes it less painless to update older worlds to new updates, as Minecraft will now attempt to seamlessly transition already-loaded chunks into new chunks that feature updated world generation and features. World blending can also affect old chunks, with new caves and underground features able to be added underneath.

Of course, one of the best PC games is also enjoying other bug fixes and polishing with this snapshot, ahead of the 1.18 update's release sometime before the end of the year. Mojang is working on finalizing the second half of the Caves and Cliffs Update, and it's up to players to thoroughly test these snapshots and provide feedback to make that happen.

The full changelog for Minecraft: Java Edition Snapshot 21w43a includes:


  • The edge between old and new world generation is now adjusted when you upgrade a world

World blending

  • When generating close to old chunks hew terrain is adjusted to better match the existing terrain at the borders
  • In old chunks, if there is Bedrock at y=0, the column below will be filled with Deepslate
    • Worlds upgraded in this snapshot will permanently have this deepslate, so if you want new caves under height 0 later, make sure to keep a backup before upgrading
  • The old Bedrock between y=0 and y=4 in old chunks gets replaced with Deepslate
  • A new Bedrock layer is placed at y=-64


  • The Priority Updates video setting has been renamed to Chunk Builder
  • Reduced the amount of flooded caves near river and ocean coastlines
  • Aquifer water levels change less often, so you'll more often have larger areas with the same water level. This means slightly fewer underground waterfalls and slightly easier underground boat travel
  • Lava aquifers are slightly less common
  • Restricted Big Dripleaf placement to Clay, Grass, Dirt, Farmland, Moss, Rooted Dirt, Podzol and Mycelium

Technical updates

  • Some internal details of block and fluid ticking have been changed to improve save times. While it should behave exactly as it was, it might be a good time to test your redstone contraptions (on a copy of a world or with a backup, of course)
  • The Chunk format has been updated

World data: Chunk format

  • Removed chunk's Level and moved everything it contained up
  • Chunk's Level.Entities has moved to entities
  • Chunk's Level.TileEntities has moved to block_entities
  • Chunk's Level.TileTicks and Level.ToBeTicked have moved to block_ticks
  • Chunk's Level.LiquidTicks and Level.LiquidsToBeTicked have moved to fluid_ticks
  • Chunk's Level.Sections has moved to sections
  • Chunk's Level.Structures has moved to structures
  • Chunk's Level.Structures.Starts has moved to structures.starts
  • Chunk's Level.Sections[].BlockStates and Level.Sections[].Palette have moved to a container structure in sections[].block_states
  • Chunk's Level.Biomes are now paletted and live in a similar container structure in sections[].biomes
  • Added yPos — the minimum section y position in the chunk
  • Added below_zero_retrogen containing data to support below zero generation
  • Added blending_data containing data to support blending new world generation with existing chunks

Fixed bugs

  • Deep warm ocean generates without coral and sea pickles
  • Badlands layers not generating properly
  • Pufferfish don't spawn in deep warm ocean
  • Deep Warm Oceans don't count towards the "Adventuring Time" advancement
  • Badlands strata is covered by orange terracotta at Y=160 and above
  • Decorators are independent of world seed
  • Stone can generate in the Nether
  • Lava pockets generate in icebergs
Zachary Boddy
Staff Writer

Zachary Boddy (They / Them) is a Staff Writer for Windows Central, primarily focused on covering the latest news in tech and gaming, the best Xbox and PC games, and the most interesting Windows and Xbox hardware. They have been gaming and writing for most of their life starting with the original Xbox, and started out as a freelancer for Windows Central and its sister sites in 2019. Now a full-fledged Staff Writer, Zachary has expanded from only writing about all things Minecraft to covering practically everything on which Windows Central is an expert, especially when it comes to Microsoft. You can find Zachary on Twitter @BoddyZachary.