Horizon vs Minecraft Java: what changes

The engine

Horizon is written in Rust and ships as its own game. It reads Minecraft Java worlds, keeps the block language, and replaces the runtime. It is not a mod loader inside Minecraft.

That is why it starts faster and why there is no Java runtime in the process. It is also why a Java mod cannot simply be dropped in.

Mods

Horizon has content mods (.hmod) and native mods (.hnmod). Content mods add blocks and items; native mods hook the engine and are compiled against a Horizon commit.

Java mods, Fabric, NeoForge and OptiFine do not run inside Horizon. Ports exist, but they are separate projects in Horizon's registry, not the Java files.

Performance

The runtime is different, but “Rust” is not a frame-rate guarantee. Your GPU, render distance, shaders and the number of entities still decide the frame time.

Performance mods such as Dynamic FPS and Fast Items help on a laptop; Distant Horizons trades memory for view distance. The pack page says which is inside.

Servers and shaders

• Servers run Horizon's server, not Paper or Spigot. Java plugins do not load.
• Server-side mods are part of the server profile; the launcher keeps client and server packs aligned.
• Shaders are .hshader files against Horizon's native shader API, not OptiFine or Iris packs.

What stays the same

Worlds and the block language travel. Your Java world can be opened by Horizon, but a redstone contraption or a farm is not guaranteed to behave identically: the simulation is a different implementation.

The account requirement also stays: Horizon checks for a Microsoft account that owns Java Edition. xHorizon does not bypass it.