Minecraft 26.4 Snapshot 1: Vulkan by default, sulfur caves in old worlds, and every change explained

Minecraft Java 26.4 Snapshot 1 released on 22 September 2026, one week after 26.3 "Wilderness Bound" and four days before Minecraft Live announced what 26.4 is for: the Ice Caves drop.

If you installed it hoping to see ice crystals and frozen zombies, you will not find them. This first snapshot has no new blocks, items or mobs. What it does have is a set of changes that matter more over time than they look on paper: Vulkan becomes the default renderer, the crash safety net that stepped you back to OpenGL is gone, worlds from before 1.18 start getting sulfur caves in their deep layers, mushrooms become placeable anywhere, and both pack formats move.

This is the full breakdown, grouped by who each change actually affects.

The short version

Where Ice Caves are

Not here yet. Minecraft Live confirmed on 26 September that Ice Caves is the next drop, with a new cave biome under cold biomes, the frozen zombie and a new freezing status effect (full details in our Minecraft Live recap). This snapshot was released before that announcement and contains none of it.

That is normal. The first snapshot of a cycle is often housekeeping and engine work, and drop features land over the following weeks. If the usual weekly rhythm holds, expect Ice Caves content to start showing up in later 26.4 snapshots.

Vulkan is now the default renderer

This is the change most players will actually notice.

In 26.2, Vulkan arrived as an experimental, opt-in renderer. The Graphics API setting had three options: Default (which behaved like OpenGL), Prefer Vulkan (Experimental) and Prefer OpenGL. We covered that setup in Minecraft Vulkan: is it worth turning on?.

In 26.4 Snapshot 1:

• Default now prefers Vulkan. It behaves the same as the "Prefer Vulkan" option. If you never touched the setting, you are now on Vulkan.
• The crash-triggered downgrade is disabled. In 26.2, if the game crashed on startup with a given graphics API, it automatically stepped down on the next launch (Prefer Vulkan to Default, Default to Prefer OpenGL). That safety ladder no longer runs.

Put those two together and the practical effect is simple: if your machine has trouble with Vulkan, the game will no longer quietly rescue you by switching to OpenGL. You have to switch it yourself.

Why Mojang is doing this

Making a renderer the default is how you find out whether it is ready. The opt-in period in 26.2 and 26.3 only reached players who went looking for the setting. Flipping the default in a snapshot puts Vulkan in front of everyone who plays snapshots, which is exactly the crowd that reports bugs. Removing the automatic downgrade serves the same purpose: a crash that silently falls back to OpenGL is a crash nobody reports.

It is also a strong signal about the release. We would not be surprised to see Vulkan become the default in the full 26.4 release, but Mojang has not said so, and snapshot defaults do change before release. Treat it as the direction of travel, not a promise.

OIT got simpler

The order-independent transparency renderer that replaced Improved Transparency in 26.3 (see our OIT explainer) was reworked. The wavelet-based math has been replaced with depth bin accumulation, a simpler approach. Two shader defines were renamed as a result:

• OIT_COEFF_COUNT is now OIT_NUMBER_OF_DEPTH_BINS
• OIT_COEFF_ATTACHMENT_COUNT is now OIT_TRANSMITTANCE_TARGET_COUNT

For players this is invisible except for possible changes in how overlapping glass, water and particles look. For shader pack and core shader authors, the renames will break anything that references the old names, so expect shader packs to need another update for 26.4.

What this means for mods

Sodium, Iris and the rest of the rendering mod ecosystem were built around OpenGL. A Vulkan default does not break them by itself, since mods can pick the backend they support, but the direction is now clear, and the OIT rewrite touches the exact render pass shader mods care about. The mod picture for 26.3 is in what breaks in 26.3; for 26.4 it is far too early, and nobody should be running a modded main world on a snapshot anyway.

A crash that silently falls back to OpenGL is a crash nobody reports. Removing the safety net is how Mojang finds out whether Vulkan is ready.

Sulfur caves now generate under old worlds

This one needs a bit of history to make sense.

When 1.18 "Caves and Cliffs" extended the world down to Y -64, Mojang added a special upgrade for older worlds: when a pre-1.18 chunk was loaded, the game generated new terrain below it, filling the new space under Y 0 with deepslate and caves. The terrain you had already built on stayed untouched. That process is called retrogen, and it is the one case where Minecraft adds new generation to chunks that already exist.

Sulfur caves, added in 26.2 "Chaos Cubed", did not take part in that. Until now, a world started before 1.18 could never get them in its old areas.

26.4 Snapshot 1 changes that. Upgrading a world from before Caves and Cliffs now also generates sulfur caves below the old chunks. It is controlled by a new biome tag, #generated_in_below_zero_retrogen, that decides which biomes the below-zero retrogen can place.

What that does and does not mean:

• It only applies to worlds from before 1.18, and only to chunks being upgraded from that era. A world created in 1.18 or later already has its deep layers, and this does not touch them.
• It only affects the below-zero section. Your surface, your builds and everything above Y 0 are not regenerated.
• It is not a general "new biomes in old chunks" feature. Dappled forests from 26.3, and Ice Caves when they arrive, still follow the normal rule: new content in new chunks. See how to find a sulfur cave for what they are once you find one.

A second, smaller world generation note: a new #is_cave biome tag was added, which gives data pack authors a single tag for cave biomes instead of listing them by hand.

Mushrooms place anywhere

Brown and red mushrooms can now be placed on any block with a solid top face, regardless of light level. Before this, a mushroom on a normal block needed low light, and placing one in a bright room just failed.

Spreading has not changed. Mushrooms still only spread in light below 13, or on blocks that support them regardless of light, such as mycelium and podzol. So a mushroom farm works exactly as before; the change is for decoration. Builders get two free decorative plants that no longer care about lighting, which is useful for kitchens, forest floors and anywhere else a mushroom looks right under a lamp.

For pack authors: new formats

• Data pack format: 122.0 (26.3 was 121.0)
• Resource pack format: 98.0 (26.3 was 97.1)

Any pack declaring the 26.3 format will be flagged as made for an older version. That alone does not mean it is broken, but this snapshot also changed world generation data in ways that will break some packs outright:

• The default_block field was removed from noise settings. The default block is now always air. Packs that set it will need to be changed.
• The cuboid placement modifier was resized: an xz_size of 2 now gives a 2 by 2 area instead of 3 by 3. Packs relying on the old sizing will place features in a smaller area than intended.
• fixed_placement now requires at least one position.
• Placed features now have XZ domain validation, enforcing the 3 by 3 chunk limit on where a feature can place blocks.
• Multi-noise biome sources reject overlapping entries.
• straight_trunk_placer gained an optional trunk_width field (defaults to 1.0), which opens the door to thicker trunks in custom trees.
• The minecraft:steep material condition was revised so badlands surfaces generate more consistently.

If you maintain a world generation data pack, test it against this snapshot now rather than at release. For general troubleshooting when a pack shows up red, see how to install datapacks.

For command and map makers

• Float to integer NBT conversion now always rounds down. Before, conversions could behave inconsistently depending on the path they took (bug MC-276879). If your commands copy float values into integer fields, results that sat on the edge may now come out one lower.
• /fillbiome works with block accuracy, instead of snapping to the coarser biome grid. That makes it much more predictable for map makers painting biomes into precise shapes.

For server admins

This snapshot has more server-side changes than usual. Three new server.properties keys:

If you are not sure where these go or what the existing keys do, server.properties explained covers the file.

The network protocol changes are aimed at proxies and server networks:

• The handshake (minecraft:intention) host field grew to 1024 characters and now understands ?key=value query syntax and an <id>@<host> form. In plain terms, the address a player types can carry extra information to the server, such as which connection ID to use.
• The minecraft:transfer packet gained a properties field to pass those host parameters along when sending a player to another server.
• SRV DNS records are now reflected in the host field, with an _o property carrying the original address. Previously, what the server saw from an SRV connection was inconsistent (MC-278651).
• A new minecraft:mod_list custom packet was added. Vanilla sends it empty; the obvious use is letting modded clients tell servers what they are running.

None of this needs action on a small vanilla server. If you run a network behind Velocity, BungeeCord or a custom proxy, this is the part of 26.4 to watch, because the handshake format is exactly what proxies parse.

Bug fixes worth knowing about

The snapshot fixes 29 bugs. The ones players will feel:

• Auto-jump near water: a cluster of long-standing bugs (MC-8959, MC-44560, MC-135211 and MC-135212) where auto-jump fired at the edge of water or lava, or when you were pushed toward it. MC-8959 dates back to the earliest bug tracker days.
• Bouncing off walls when jumping into water (MC-50749).
• Item frames: items dropping upside down from ceiling frames (MC-123848), and several update and sync issues (MC-296053, MC-311265, MC-311788).
• Armor stands: rotation issues and a creative mode duplication bug (MC-311195, MC-311473).
• Vulkan: a depth attachment format bug (MC-310767), fixed just in time for Vulkan to become the default.
• Mushroom placement lighting restrictions (MC-311773), resolved by the placement change above.
• Smaller fixes for minecart audio, wolf armor, a spectator mode issue, tooltip text and item model rendering gaps.

Should you play it?

How to install the snapshot

1. Open the Minecraft Launcher and go to Installations.
2. Enable Snapshots in the version filter.
3. Create a new installation with 26.4 Snapshot 1 (the launcher also offers "Latest snapshot", which updates itself every week).
4. Set a separate game directory for it, so snapshot worlds and options never mix with your main install.
5. Play in a new world or a copy of an existing one.

Frequently asked questions

When was Minecraft 26.4 Snapshot 1 released?

On 22 September 2026, one week after 26.3 "Wilderness Bound".

Does 26.4 Snapshot 1 have Ice Caves?

No. Ice Caves, the frozen zombie and the freezing effect were announced at Minecraft Live on 26 September, after this snapshot. They are expected in later 26.4 snapshots.

Is Vulkan the default in Minecraft now?

In the 26.4 snapshots, yes: the Default graphics API now prefers Vulkan. In the current release, 26.3, Vulkan is still opt-in.

How do I switch back to OpenGL?

Video Settings, Graphics API, Prefer OpenGL. The game will no longer do this for you automatically after a crash.

Will my old world get sulfur caves?

Only if it was created before 1.18, only in chunks being upgraded from that era, and only in the new deep layers below Y 0. Worlds made in 1.18 or later are not affected.

What is the data pack format for 26.4 Snapshot 1?

122.0. The resource pack format is 98.0.

Does 26.4 Snapshot 1 need a new Java version?

No. It requires Java SE 25, the same as 26.2 and 26.3.

What comes next

Weekly snapshots should now start bringing Ice Caves content in pieces: the biome, ice crystals and icicles, the frozen zombie, ice balls and the freezing effect. We will test each one as it lands and publish guides only once there is something real to test. For the bigger picture of where Minecraft is going, including the Sift dimension arriving in 2027, read our Minecraft Live September 2026 recap.