7:38pm: The AP has the details: Kotsay makes a base salary of $1.5MM, but he gets $200K if he makes 300 plate appearances and an additional $200K for every 50 times up after that, up to 500 plate appearances. He could make up to $1MM on top of his base salary.
3:59pm: According to Art Martone of the Providence Journal, the Red Sox announced the Mark Kotsay signing today. He gets a one-year deal. The Sox also designated reliever David Aardsma for assignment.