Hi in Russian

Привет goes exactly as far as ты does: friends, family, classmates, children, anyone who has offered you the informal you. The moment a stranger, an official or an elder is involved, the greeting switches to здравствуйте along with the pronoun; the two boundaries always move together.

In messages the casual register loosens further: приветик softens, хай is quick thumbs-up energy, and здорово arrives with how-are-things energy, usually as здорово, как сам? Nobody will mind if you never use them; everybody will notice if you use them with the wrong person.