Yes, AI is a Scrabble word!

Letter values in Scrabble US: A 1, I 1.

Is it a valid word?

AI is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an agency of the United States Army responsible for providing timely and relevant and accurate and synchronized intelligence to tactical and operational and strategic level commanders
the branch of computer science that deal with writing computer programs that can solve problems creatively
a sloth that has three long claws on each forefoot and each hindfoot
the introduction of semen into the oviduct or uterus by some means other than sexual intercourse

Also: army intelligence, artificial intelligence, three-toed sloth, bradypus tridactylus, artificial insemination.