Marcus Thompson of the Bay Area News Group reported the deal would be worth $25 million over four years.
The Akron Beacon Journal's Jason Lloyd reported the fourth year would be a team option.
NBA insider David Aldridge seemed to at least confirm Jack's on his way to Cleveland after speaking with the guard. Mike Brown was apparently the deciding factor.
Tristan Thompson is already welcoming Jack to the team.
The Cavs have a ton of cap space, so it was going to be interesting to see how they would spend it this offseason. Cleveland is building around a core that includes young players like Thompson, Kyrie Irving, Dion Waiters and 2013 No. 1 overall pick Anthony Bennett.
With those young players, it was unlikely that general manager Chris Grant would want to splash a lot of cash on a high-priced veteran.
Jack is a nice fit for a team that already has the best young point guard in the game with Irving. Jack is not the kind of player you'd want as your starter, but he can be very effective coming off the bench.
Backing up Stephen Curry, Jack averaged 12.9 points and 5.6 assists last season for the Golden State Warriors.
ESPN's Brian Windhorst reported what Jack would bring to the Cavs.
One of Irving's biggest problems has been health. Of the Cavs' 148 games over the last two seasons, Irving has missed 38.
With Jack possibly in the fold, Cleveland doesn't have to worry about a massive drop-off when Irving misses time. Plus, only once in eight seasons has the 29-year-old Jack played in fewer than 79 regular-season games.
Jack is exactly the kind of complementary part who will add production and experience to the Cavaliers while not commanding a ton of time on the floor nor a huge chunk of the cap.