The one-year contract is worth $3.25 million, sources told ESPN. It could reach $3.5 million with incentives, according to a source.
The former New England Patriots linebacker tweeted of the deal:
- brandon spikes (@BrandonSpikes55) March 15, 2014
Spikes had 86 tackles and an interception last season, the former Florida player's fourth with the Patriots. He's rejoining former Pats linebackers coach Pepper Johnson, the Bills' new defensive line coach.
Spikes is regarded as a key addition for a defense that struggled against the run last season and is under transition with Jim Schwartz taking over as coordinator. Schwartz replaces Mike Pettine, who left Buffalo after one season to take over as Cleveland's head coach.
The deal with Spikes will allow the Bills to move Kiko Alonso to an outside role, a position to which they believe he's best suited.
Buffalo allowed 150 or more yards on the ground seven times last season. That was a glaring weakness for a defense that was solid in other areas with a franchise-record 57 sacks and that finished 10th in the NFL in yards allowed, Buffalo's best finish since ranking second in 2004.
Dixon ran for 458 yards and eight touchdowns in four seasons San Francisco but dropped down the depth chart behind Frank Gore and Kendall Hunter. Dixon played some at fullback after Bruce Miller was injured.
ESPN NFL Insiders Adam Caplan and Adam Schefter and The Associated Press contributed to this report.