Update 4 was released on July 7, 2019, at a time when 
Blox Fruits was still a very young game. It adds the 
Sand fruit and the 
Dark Blade V2 progression, but its real focus is cleanup: an extensive series of hitbox corrections and combat glitch fixes, plus a first batch of balance adjustments.
How to get it
Released on July 7, 2019. It's one of the very first game updates, described by the Fandom as focused on fixes and balancing, with a little new content.
New Features
- New Blox Fruit: Sand
- New progression: Dark Blade V2
Fixes
Buddha hitbox fixed against area-of-effect attacks.
Aura now works correctly with Buddha and 
Rubber.
Bisento V2 hitbox fixed.- Dual weapon equip glitch fixed, such as having a gun and sword equipped at the same time.
- Likely fix for combat breaking after death.
- Menu buttons that were randomly breaking fixed.
Game Passes purchased from the in-game shop are now activated instantly.- Bisento's X move no longer blocks the player.
- Buddha weapon hitboxes that weren't always registering are now fixed.
Buffs
Phoenix
LightNerfs
Rabbit: now grants only 15% speed bonus in Buddha form, down from 60% previously.- Dark Blade V2: X move hitbox reduced.
Other Changes
Dark Step idle animation modified.
Fruit Notifier Game Pass added.- Added a way to spend stat points faster.
- Added a system preventing players from finding too many fruits in a short amount of time.
- The Fandom also mentions other minor changes without detailing them.