---
title: "Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+ in Prism Launcher — Setup & JVM Flags"
description: "Configure Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+ (Eclipse Adoptium Temurin 21 / Microsoft OpenJDK 21) in Prism Launcher for Minecraft 1.20.5, 1.20.6, 1.21 – 1.21.4+. Recommended JVM arguments: -XX:+UseG1GC -XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=20."
canonical: https://prismlauncher.ink/java/java-21-temurin-minecraft-1-20-5-1-21
updated: 2026-10-17
---

# Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+

Mojang upgraded Minecraft 1.20.5 and 1.21+ to require a 64-bit Java 21 runtime; launching with Java 17 or Java 8 causes an immediate incompatible class version crash. Applies to Minecraft 1.20.5, 1.20.6, 1.21 – 1.21.4+.

## Facts (2026-10-17)

- **Configuration:** Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+
- **Minecraft Range:** Minecraft 1.20.5, 1.20.6, 1.21 – 1.21.4+
- **Recommended Build:** Eclipse Adoptium Temurin 21 / Microsoft OpenJDK 21
- **JVM Flags:** -XX:+UseG1GC -XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=20

## Why Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+ matters for Minecraft 1.20.5, 1.20.6, 1.21 – 1.21.4+

Mojang upgraded Minecraft 1.20.5 and 1.21+ to require a 64-bit Java 21 runtime; launching with Java 17 or Java 8 causes an immediate incompatible class version crash.

Inside Prism Launcher, open **Settings** → **Java** (or override per instance under **Edit Instance** → **Settings**) and click **Auto-detect** or **Download** to select `Eclipse Adoptium Temurin 21 / Microsoft OpenJDK 21`.

## Recommended JVM flags and memory checks

- **JVM arguments:** `-XX:+UseG1GC -XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=20`. Always click **Test** in the Java settings panel to verify the runtime passes Prism's architecture check.
- **64-bit verification:** Ensure the architecture column reads `x86_64` (or `arm64`), never 32-bit `x86`, so you can allocate more than 2 GB of RAM.
- **Download launcher:** Get the latest Windows build of Prism Launcher from [/download](https://prismlauncher.ink/download).

## FAQ

### Which Minecraft versions need Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+?

It is designed for Minecraft 1.20.5, 1.20.6, 1.21 – 1.21.4+.

### Can Prism Launcher keep Java 8, Java 17, and Java 21 installed at the same time?

Yes. Prism Launcher lets you assign a different Java executable to each individual instance.

## Related

- [Prism Launcher Java & JVM Configuration](https://prismlauncher.ink/java)
- [Complete Minecraft Java Version Chart (Java 8, Java 17 & Java 21)](https://prismlauncher.ink/java/which-java-version-for-each-minecraft-version)
- [How to Fix Minecraft Exit Code 1 & Exit Code -1 in Prism Launcher](https://prismlauncher.ink/howto/fix-minecraft-exit-code-1-prism-launcher)
- [Prism Launcher Windows Setup & Installation](https://prismlauncher.ink/setup)
- [Troubleshooting: Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+](https://prismlauncher.ink/java/java-21-temurin-minecraft-1-20-5-1-21-troubleshooting)

## Download

Free and open source: [Download Prism Launcher](https://prismlauncher.ink/download)

Markdown mirror: https://prismlauncher.ink/java/java-21-temurin-minecraft-1-20-5-1-21.md