This is shocking news and very unexpected.
The new Raider has 39 career sacks in 111 games.
The Patriots have confirmed the deal and released this statement from Patriots head coach Bill Belichick:
"From nearly the day he arrived in 2001, Richard Seymour established himself as one of our premier players for nearly a decade. His presence has been felt as a force on the field, a respected man off it and a multi-year champion.
"Any transaction we make is with the goal of what is best for our team and, as difficult as it is to part ways with a player of Richard's stature, many factors were taken into account when we considered this trade. As an organization, we feel the trade with Oakland brings sufficient value and is in the long-term interest of the club. We are extremely grateful for the huge impact Richard's elite level of performance had on our success and we wish him the very best during the rest of his career."
With this deal, New England opens up $3.6 million on the salary cap to perhaps continue contract negotiations with defensive lineman Vince Wilfork.
UPDATE: The Patriots wasted no time filling the open roster spot left behind by Seymour. They signed former first-round offensive lineman Kendall Simmons.