Terralith and TerraBlender: why Superflat, Amplified and Large Biomes get ignored

What happens

You start a new world, open the world type screen, and pick Superflat, Amplified, or Large Biomes. The world creates without complaint. Then you spawn in and the terrain is ordinary: Superflat gives you rolling hills instead of flat layers, Amplified gives you normal height variation instead of exaggerated peaks, Large Biomes gives you regular sized biomes instead of the stretched out version the preset promises. No error, no warning, no log entry. The preset you picked is simply not what generated.

Players hit this constantly with Terralith and describe it the same way across CurseForge comments: a Superflat world that "ignored the superflat preset and set it to normal world," a request for a flat water world that "just creates a normal world," a report that "this mod ignores single biome worlds" too. Every one of those is the same underlying failure, not four separate bugs.

Which mods this affects

TerraBlender is a library mod that several biome mods build on. It intercepts the overworld's normal biome placement and weaves in extra biomes supplied by whichever mod depends on it, using the same data driven approach a raw worldgen datapack uses for its content. Terralith's own maintainer put it plainly in the mod's GitHub issue tracker: "Terralith is a datapack, yes, even the mod version, it is a datapack packaged as a mod." That description holds for TerraBlender based biome content generally, which is why this is not unique to one mod. Biomes O' Plenty's TerraBlender integration and William Wythers' Overhauled Overworld add biomes through the same kind of mechanism and run into the same limitation.

Why it happens

World type selection happens before any datapack content gets applied. Choosing Default, Superflat, Amplified, or Large Biomes tells the game which chunk generator configuration to load for the overworld, and that choice is settled first. A worldgen datapack, which is what Terralith and any TerraBlender based mod ship at the core, only extends the biome list wired into the Default configuration. It has no hook into the separate configurations the alternate presets use.

Superflat is the clearest case: it does not place biomes by noise at all. It stacks a fixed set of block layers and uses one chosen biome for the whole world, so there is no noise based biome list for a datapack to add to. Amplified and Large Biomes do use noise based biome placement, but historically through their own separate preset data rather than the Default configuration a worldgen datapack extends.

Terralith's maintainer traces this to a genuine Minecraft engine limitation, not a mistake in the mod, and links it to a Mojang bug tracker ticket, MC-260949. The specific gap was the inability for a datapack to define a custom biome parameter list for anything other than the Default preset. Until that capability existed, there was no legitimate way for any worldgen datapack, from any mod, to reach Large Biomes or Amplified generation at all.

The fix, and its limits

Mojang eventually added that capability, and Terralith 2.6.0 uses it: Large Biomes and Amplified generate correctly with Terralith's biomes on Minecraft 1.21.1, 1.21.11, 26.1, and everything after. That fix is not backported, so any older instance stays affected regardless of the mod version installed on it. Superflat sits outside the fix entirely, for the reason above: no biome parameter list capability changes what a layer stacking generator with no noise placement can do.

Other TerraBlender based mods do not inherit Terralith's fix just by sharing the library. Each mod owns its own biome data and has to update it separately to take advantage of the same underlying capability.

Why this belongs on a version-tracking site

Neither TerraBlender's documentation nor most biome mods' own pages spell out which world types they support, because from the perspective of a single mod's changelog, "does not work with Superflat" reads like a footnote rather than a headline. It only becomes visible as a pattern once you line up several mods that share the same dependency and watch them fail the same way, on the same presets, for the same reason, tracing back to one Mojang bug ticket. That is exactly the kind of fact that belongs in a compatibility reference rather than any one project's own notes: precise, dated, tied to a specific version boundary, and true regardless of what any individual mod's next release does.