FLauncher 12.1.0 — Optimization Suite

FLauncher 12.1.0 — Optimization Suite

New Performance section in Settings → Minecraft (and per-instance under Settings, with the override checkbox). Everything is off by default — if you don't touch it, launches are identical to 12.0.4.

Auto-optimized JVM flags

Tuned garbage-collector flags chosen for your Java version and RAM:

• Balanced (G1) — recommended for everyone. On Java 8 / MC 1.8.9 this replaces the default collector responsible for the classic periodic stutter with short, predictable pauses.
• Low latency (ZGC) — for Java 21+ with a 6 GB+ heap and 16 GB+ RAM; silently falls back to Balanced otherwise.

These target stutter and frame-time consistency, not average FPS. Anything you set yourself in the Java arguments box overrides the generated flags.

Automatic memory sizing

Picks -Xmx from your installed RAM and the game's Java generation (2–3 GB for 1.8.9-class, 4 GB for modern MC, never more than half your RAM). With RAM to spare it locks the heap size at startup to eliminate resize hitches. A per-instance Memory override always wins.

Game process priority (Windows)

Optionally run the game at Above normal (recommended) or High priority so background apps steal less CPU. Not applied when a wrapper command is set.

Notes

• Very old Java 8 builds (below update 40) may reject the tuned flags and exit at startup with a clear message in the log — disable the toggle if that happens; a guard ships in the next release.
• Auto-update from 12.0.x works as usual.