Minecraft 26.4 Snapshot 6: Snow Bricks, a Sulfur Cube That Freezes Water, and Three Crash Fixes

Mojang shipped Minecraft 26.4 Snapshot 6 yesterday, and after last week's protocol rewrite and Java version bump, this one is a relief. There is nothing in here that breaks your proxy. It is a building snapshot with a handful of server-side fixes attached, and a couple of those fixes are worth updating a test server for on their own.

Snow Bricks Are the Set Snow Should Have Had Years Ago

Four Snow Blocks in a 2x2 gives you Snow Bricks, and the family arrives complete: slab, stairs and wall on day one. That is the second snapshot running where a new block set has shipped whole rather than drip fed across a drop, which is a pattern worth noticing if you build at scale.

Two caveats attached to it, and both are deliberate.

The first is that a Stonecutter will not cut the slabs, stairs or walls. Every other brick family in the game lets you skip the crafting grid and avoid waste. This one does not, so you are back to crafting recipes and the conversion losses that come with them. Budget more Snow Blocks than you think you need.

The second is that Snow Bricks only drop themselves when mined with a Shovel. Hit one with a pickaxe or your fist and you get nothing. That is consistent with how snow has always behaved, but it is the sort of detail that costs someone a chunk of a build the first time they break one on autopilot.

There is also a line in the changelog that is easy to skim past: Snow Bricks belong to the Fast Sliding Sulfur Cube archetype. So the block is not purely decorative, it is also an input to the cube system that 26.4 has been building out since the drop began.

The Cold Sulfur Cube Freezes Its Own Road

The genuinely new mechanic this week is the Cold Sulfur Cube, a special-category archetype you get by having a Sulfur Cube absorb a Blue Ice block.

It has the same properties as the Fast Sliding archetype, with one addition: it floats, and when it moves across water it replaces the block below with a disk of Frosted Ice, the same way the Frost Walker enchantment does under a player's feet.

Two conditions govern it. There has to be air above the water for the Frosted Ice to be placed, and the cube only does it if it starts its movement on the ground. So it is not an unconditional water-to-ice converter, and you cannot drop one into the middle of an ocean and expect a bridge.

For survival servers, think about what that means on a lake near spawn. Frosted Ice melts, so this is not permanent terrain damage, but a cube wandering a shoreline will keep flickering a body of water in and out of ice. If you run a build world or a themed map with water features, this belongs on your list of things to test before 26.4 goes live rather than after.

On the data pack side, Sulfur Cube Archetypes gained an optional location_based_effects field, taking the same format as a location-based enchantment effect, with level-based values always evaluated at level 1. There is a matching item tag, #sulfur_cube_archetype/cold, so you can define what else turns a cube cold.

Brittle Ice Finally Obeys Your Server Rules

This is the part that matters most if you are running a server, and it is buried in the bug list rather than the changes section.

Brittle Ice arrived in Snapshot 4 and shipped with two holes in it. MC-312574 let entities crack and destroy it even with the mob_griefing gamerule set to false. MC-312576 let players crack it inside spawn protection. Both are fixed.

If you had written off brittle ice as unusable near spawn or in a protected build, that reasoning no longer applies. The two mechanisms server owners rely on to make an area safe now cover it.

Four more brittle ice fixes round it out. Strays no longer crack it just by standing on it, which was making ice cave spawns self-destructive. Shulkers now do crack it, which they were not. Lily pads can be placed on it. And iron golems summoned by villagers can no longer spawn on it, which was producing golems that fell through the floor seconds after arriving.

Three Crashes, and Two of Them Are Staff Problems

Three crash fixes this week, and the pattern across them is worth flagging because they all involve opening a screen in a state that is normal on a multiplayer server and rare in single player.

• MC-312270: the game crashed when you opened the inventory while spectating a mob. Anyone moderating in spectator mode was one keypress from a crash.
• MC-312579: the game crashed when you opened the inventory with a below_name scoreboard objective active. That is a display slot used by a huge number of servers for health, levels and kill counts, so this one had a wide blast radius.
• MC-312665: the game crashed in the pause menu when the music toast was showing and the track could not be played.

If you have players on snapshots and have been seeing crash reports you could not reproduce, check those three before you go hunting through your plugin list.

Packed Ice Bricks Now Need a Pickaxe

Worth a correction on last week. When Packed Ice Bricks landed in Snapshot 5, they always dropped themselves regardless of tool, and that was part of what made them feel like such an unusually generous building block.

That has changed. All Packed Ice Brick variants now require a pickaxe to be mined in order to drop themselves. Still no Silk Touch, still not slippery, still does not melt, so the block is as good as it was for building. But the no-tool harvesting is gone, and if you wrote a server guide or a wiki page in the last week, that line needs editing.

The Game Now Picks Its Own Heap Size

The default JVM options have changed. The game now sets its Java heap size automatically from your system RAM, using up to 25 per cent with a ceiling of 4 GB.

This is about the game's own defaults, not your server jar, and your existing startup flags are untouched. But it is a change your players will feel. Anyone who never touched their allocation and was running on whatever the launcher handed them is now on a sensibly scaled heap rather than a fixed number, and on a 16 GB machine that is 4 GB instead of the old default. For a vanilla client that is comfortable. For a heavy resource pack or a big render distance it is still worth a manual bump, and "give it more RAM" remains support answer number one.

In the same area, mobs falling through lava may now take slightly less fall damage in some cases.

Data Pack 125.1: Terrain Tools Get Interesting

The data pack format is now 125.1, the resource pack format 101.0, and the world generation additions are the most substantial part of the technical changes.

The gradient density function now accepts a Vertical Anchor for from_coordinate and to_coordinate, as long as axis is y. Small change, but it lets you anchor a gradient to world height rather than hardcoding block numbers, which is exactly what you want when the same pack has to work across dimensions with different build limits.

The bigger addition is domain_warp, which samples an input function while applying an offset to each sampled coordinate. It takes input plus any combination of offset_x, offset_y and offset_z, each a density function in its own right, each truncated to an integer, defaulting to 0.0, and at least one of the three must be specified. Domain warping is how you get terrain that twists and folds rather than looking like noise laid over a grid, and it has been a gap in the vanilla toolkit for years.

Mojang attach an explicit warning to it: if the offsets change rapidly by a large amount, performance may degrade significantly, and it should be used sparingly. Take that seriously. World generation cost lands on your server tick, and a warp function used carelessly across a whole dimension is the kind of thing that only shows up as lag once a hundred players are exploring in different directions.

Structure Pool Elements also gained an optional corner_constraint field, which limits where a pool element can be placed by sampling a density function at the corners of its bounding box. You give it a density_function, an acceptable_density range, a padding value from 0 to 8, which corners to check (all, top or bottom), and how many required_corners must fall inside the range. That is a precise way to stop a structure piece generating half out of a cliff, which has been one of the more annoying limits of jigsaw structures.

New Tags, and One Removed Model

Three tags land this week, all of them the kind of thing data pack authors have been approximating by hand:

• #swimmable on fluids, for fluids players can swim in.
• #swimming on entity types, for entities considered to be swimming in water.
• #flying on entity types, for entities considered to be flying.

Also: icicles and sulfur spikes are now part of #dangerous_for_teleportation alongside pointed dripstone, courtesy of MC-312632. Chorus fruit and enderman teleports will stop dropping things onto spikes.

On the resource pack side, there is a new block/snow_bricks.png texture and a new block.ice_crystal.ambient sound event, with ice crystals now making ambient noise when they sit above a block of packed ice. The one to check is the removal: the block/cube_top block model is gone. If your pack or a pack you ship to players inherits from it, that is a silent break waiting on format 101.0.

Other Fixes Worth Flagging

Forty-odd fixes in total. The ones with consequences beyond the single bug:

• MC-312592 and MC-312629 fix gravel blobs generating in a changed order, which was causing feature order cycles in data packs, and ice caves generating gravel, diorite and andesite blobs twice over. Both affect newly generated chunks only.
• MC-312783 stops consumable and equippable items losing their default sounds after a world upgrade, which was fallout from Snapshot 5 making those sound fields optional.
• MC-311994 fixes delayed block breaking completing early or stalling, and MC-312450 stops a block reappearing briefly if you jump just before breaking it. Both are latency-adjacent and both are more visible on a server than offline.
• MC-312606 stops sculk sensors firing every time a jukebox playlist switches discs automatically, which would have quietly ruined any redstone built near a music setup.
• MC-312780 restores oak, birch, spruce and jungle trees converting the block below their trunks into dirt. Tree farms on non-dirt ground were behaving differently without anyone announcing it.
• MC-312804 is listed as fixed but worded as ongoing: some villager trades still unexpectedly differ from 1.21.11. If you run an economy that depends on trade rates, keep watching this one through the rest of the snapshot cycle.

Where This Leaves Things

Snapshot 6 is the quiet one in a loud cycle. No protocol changes, no Java requirement moving, nothing that stops your proxy connecting. Builders get a snow set and a cube that freezes water. Data pack authors get domain warping and corner constraints, which are the most capable terrain tools vanilla has shipped in a while.

For server owners the update is three crash fixes and brittle ice finally honouring mob_griefing and spawn protection. That is a better week than last week, when the job was auditing proxies and chasing a Java 25 runtime out of your host.

Two things to action. Check whether any resource pack you hand to players inherits from block/cube_top, because that model is gone. And if you are mid-way through writing anything about Packed Ice Bricks, the tool requirement changed underneath you.