According to the Washington Times, Lannan will earn the team's offer of $5 million for 2012 instead of the $5.7 million he had requested. It was baseball's first arbitration decision of the year.
Lannan led Washington in wins last season, posting a 10-13 record with a 3.70 earned run average in 33 starts.
The 27-year-old lefty owns a career mark of 38-51 with a 4.00 ERA in 128 starts. He has made at least 25 starts in each of the past four seasons after coming up for six games in 2007.