Display: Larger, brighter (3000 nits), LTPO3 OLED with more frequent always-on refresh (1Hz), better off-angle viewing.
Performance: New S10 chip, faster 5G, better satellite features (SOS, messaging), improved charging (0-80% in 45 mins).
Battery: Up to 42 hours normal use, better than Ultra 2, but still needs charging every few days.
Durability: Titanium case, sapphire crystal, IP6X dust resistance, WR100 (dive-ready).
Health: ECG, Blood Oxygen, new hypertension notifications (requires data, not real-time diagnosis), improved sleep tracking (simpler score).
Action Button: Customizable physical control for workouts, flashlight, etc...
GPS: Dual-frequency GPS (L1+L5) for accuracy, but can underreport distance in tunnels.