Minecraft: Java Edition Snapshot 21w39a adds new Advancements to the '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

  • Minecraft: Java Edition has a long-running "snapshot" program that tests future updates and changes before they're released.
  • The latest run of snapshots focuses on 1.18 'Caves and Cliffs Update' Part Two, a major release coming later this year.
  • Minecraft: Java Edition Snapshot 21w39a is now available to testers, and includes a solid batch of changes to test.
  • Most notable is the addition of some new Advancements for the 'Caves and Cliffs Update,' as well as changes to how effects are displayed.

Mojang Studios is continuing their work on the upcoming 1.18 Caves and Cliffs Update Part Two release, culminating in the new Minecraft: Java Edition Snapshot 21w39a being released to testers on PC. Today's release doesn't include mind-boggling new features or additions, but does begin to add new Advancements from the Caves and Cliffs Update, as well as makes some important changes.

The new Advancements aim to encourage players to approach Minecraft from interesting angles, such as falling from the very top of the newly increased world height all the way to the very bottom of the newly increased world depth, or trading with a villager while perched at the uppermost limits of the new Minecraft world heights. This snapshot for one of the best PC games follows its snapshot predecessor as the third official snapshot for 1.18 Caves and Cliffs Update Part Two.

The upcoming release will undoubtedly provide inspiration for the next era of Minecraft toys and gifts, so it's important that Mojang tests the update thoroughly ahead of an official release. If you're a part of this testing process, bear in mind that there is a known issue in this build, which highly recommends you back up any worlds before loading them under this snapshot.

The full changelog for Minecraft: Java Edition Snapshot 21w39a includes:

New features

  • Added 1.18 Caves and Cliffs Update Part Two Advancements


  • Added "Caves & Cliffs" for falling from top to bottom of the Overworld
  • Added "Feels like home" for riding strider on lava for 50 blocks in the Overworld
  • Added "Star Trader" for trading with a villager at the build height limit
  • Added "Sound of Music" for playing music with a jukebox in a Meadow biome

Known issues

  • It's highly recommended that you back up your world before loading it in this snapshot
  • New chunks won't be able to be blended into adjacent old chunks once world edge blending is added


  • The lone trees in Meadows now always contain a bee nest
  • Drowned can spawn in aquifers inside dripstone caves
  • Zombies don't spawn in dripstone caves
  • Buried treasure chests can now contain water breathing potions
  • Changed default brightness to 50
  • Redesigned how effects look in the inventory screen, to allow them to show even with the recipe book open


  • Your list of effects are now shown to the right of your inventory, instead of the left side
  • When the inventory effects list is visible, it will be hidden from the game view to reduce screen clutter
  • There are now two modes of seeing the effect list: compact and classic
    • Classic is the pre-existing list of effects, one after another
    • Compact is a single icon for each effect, suitable for small screen estate
  • The game will automatically switch between the two looks to suit the available screen estate (including having the recipe book open)

Technical updates

  • Added fall_from_height and ride_entity_distance Advancement triggers
  • Changed nether_travel to match other similar triggers
  • Added new loot table function set_potion
  • Changes to the on-disk chunk format
  • Resource pack format has been increased to 8
  • Standalone server.jar now bundles contains individual libraries instead of being flat archive


  • fall_from_height — Triggered when a player lands after falling
  • Conditions:
    • player — a player for which this trigger runs
    • start_position — location predicate for last position before falling started
    • distance — predicate for distance between start_position and player
  • ride_entity_in_lava — Triggered for every tick when player rides in lava
  • Conditions:
    • player - a player for which this trigger runs
    • start_position - position where riding started (first tick on lava)
    • distance - predicate for distance between start_position and player
  • nether_travel
    • entered condition renamed to start_position
    • exited has been removed, since it was identical to player.location

Loot tables

  • set_potion — Sets Potion tag on any item
  • Parameters:
    • id - potion id

World data: Chunk format

  • Chunk's Level.Sections[].BlockStates & Level.Sections[].Palette have moved to a container structure in Level.Sections[].block_states
  • Chunk's Level.Biomes are now paletted and live in a similar container structure in Level.Sections[].biomes
  • Chunk's Level.CarvingMasks[] is now long[] instead of byte[]

Resource pack format

  • minecraft/textures/gui/container/inventory.png now contains an extra sprite for a thin-layout version of the effect list in the inventory

Server building

  • server.jar now bundles individual libraries instead of merging all the files into single archive
  • This change is meant to solve certain problems related to Java modules
  • On startup, server.jar will unpack libraries into a directory configured by bundlerRepoDir (default: working directory)
  • To run different main class than server, use bundlerMainClass property (for example java -DbundlerMainClass=net.minecraft.data.Main -jar server.jar --reports) or unpack jar manually and use contents of META-INF/classpath-joined for command line

Fixed bugs

  • Status effects aren't displayed in inventory when recipe book is open
  • Bottom border on status effect displays in the inventory is missing
  • Status effect bars shift the player's inventory in creative mode
  • Potion effects obtained in creative mode while in inventory do not show up until reopening inventory
  • Bamboo generates in caves under jungles
  • Sugar cane generated in cave
  • Chatting causes lag to occur
  • "Feature Placement" Crash / java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0
  • Naturally generated cave vines have an age between 17-25
  • Certain Biome Builder debug values do not change
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.