Awasthi is a surname.
They are known to be the residents of ancient land of Awadh and their gotra being Upamanyu. Upamanyu was indoctrinated in the school (of thought) of Rishi Vashistha. The surname Awasthi is likely to be a derived from of “Awadhi-Vashist”. The mother tongue of Awasthi Brahmins is Awadhi, an Indo-Aryan language. Ramcharitmanas was written by Tulsidas in Awadhi language.