The team confirmed the move this afternoon.
A first round pick by San Francisco in 2008 draft, Balmer has been unexcused from 49ers training camp since Wednesday, and apparently did not want to return to the team.
Former San Francisco general manager Scot McCloughan, now with Seattle's front office, was with the team when the Niners selected Balmer with the No. 29 overall pick.
Balmer could add depth for Seattle inside, so it will be interesting to see what moves the team makes to free up a spot for Balmer.
Update: Jason La Canfora of the NFL Network is now reporting that the Seahawks likely will give up a late-round pick.
Update: Matt Maiocco of Comcast Sports.net is now reporting the Seahawks will give San Francisco a sixth-round pick.