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What Java version does Minecraft 1.21.3 need?

Java 21

Minecraft 1.21.3 was released on 2024-10-23. Mojang's version file lists Java 21 for it, for both the game and a server.

FabricYes
ForgeYes
NeoForgeYes
Top mods listing 1.21.3298 of 500

See which Java you have:

java -version

Download Java 21 from Adoptium