Green’s Dictionary of Slang

(US teen) goodbye, ‘see you later’.

2001		Eble Campus Sl. Fall 8: ONE—goodbye; concluding remark at parting that indicates a peaceful departure.
2002		Teen Lingo: The Source for Youth Ministry 🌐 one Primarily used as a phrase of dismissal to say as you are leaving or going away. As to say ‘bye or see you later.’ ‘Yo shorty you goin home......aight one.’ or on the phone. ‘Yo, I gotta go.’ ‘Aight, later, one.’ ‘One.’.