The 23-year-old forward briefly revealed on Friday evening that a deal had been done before removing the confirmation from his personal website.
But it appears there has been no late hitch and the United States international is set to undergo a medical on Monday ahead of signing a permanent contract at the Stadium of Light.
Altidore spent time on loan in the Premier League with Hull City back in 2009/10, scoring one goal in 28 appearances.
But his reputation has blossomed since then and the powerful player registered 31 goals for AZ in all competitions last season.
His arrival is just the latest in a series of acquisitions by Black Cats boss Paolo Di Canio as he looks to overhaul a squad that came perilously close to relegation from the top flight in May.