According to ESPN, the three-year deal is worth $11.75 million, including $4 million guaranteed.
The signing of Whitner, 26, could signal that the 49ers intend to part ways with Taylor Mays, a second-year pro, and Dashon Goldson, a starter the last two seasons. The 49ers agreed to a one-year contract with safety Madieu Williams earlier in the week. Williams, 29, was released by the Minnesota Vikings last week.
Goldson acknowledged the inevitable with his own tweet: "Sorry guys thanx for all ur support but not gonna be back. See ya"