DOT 3 and DOT 4 brake fluid question

I normally use DOT 3 brake fluid. A friend gave me some chemicals and in it was a bottle of DOT 4 brake fluid. Are the types compatible with each other?

Yep DOT 4 has a higher boiling point thats all

Completely compatable. These days I see no reason to ever buy DOT3 again (haven't bought it in many years, never bought silicone DOT5) just my preference

Do not use it if its been opened brake fluid is hydroscopic sp? and will soak up moisture from the air. Never buy more than you need, toss and left overs