The Royals bought out the contract for $750,000.
Soria missed all of the 2012 season after undergoing Tommy John surgery on April 3 and general manager Dayton Moore has indicated the right-hander might not be ready to pitch in the Major Leagues until June.
Moore also has indicated that the Royals are interested in negotiating a new deal with Soria, probably laden with incentives based on his ability to return to pitching.
On Wednesday, Moore said he couldn't comment on any negotiations with Soria.
"I think I've been very candid and clear that we love Joakim, his 160 saves and everything he's meant to our organization, and we believe in him," Moore said. "We'll do everything we can to make sure we stay in the game in regards to where he ends up. But he's going to explore free agency, and we're just going to see where it unfolds."
Soria, 28, was a story of success from the Rule 5 Draft of Dec. 7, 2006. Plucked from the Padres' organization, Soria became the Royals' closer midway through his rookie year of 2007 and over five seasons developed into one of the premier save artists in the game.
Through 2011, he had 160 saves, a 2.40 ERA and a 13-15 record in 298 relief appearances with the Royals. This year he was replaced in the first half by Jonathan Broxton, who had 23 saves before he was traded to the Reds, and in the second half by Greg Holland, who had 16 saves.
Based on his strong showing, Holland is expected to start 2013 as the Royals' closer.
Soria agreed to a multi-year deal that paid him a base salary of $8.75 million spread over 2009-11 and the Royals picked up his option at $6 million for 2012. Including this year, there were three more club options.
His best seasons were 2008, when he had 42 saves and a 1.60 ERA, and 2010 with 43 saves and a 1.78 ERA. After becoming the full-time closer on July 31, 2007, he converted 150 of 167 save opportunities. A career high of seven blown saves came in 2011 when he slipped to 28 saves with a 4.03 ERA.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.