Stafford spoke in vague terms about his new deal Tuesday after details were reported by the Detroit Free Press and Crain's Detroit Business.
The Detroit Free Press reported Stafford and defensive end Kyle Vanden Bosch, who also restructured his contract, helped the Lions clear about $8.5 million in cap space.
Both players converted reduced base salaries into signing bonuses to be paid over the remaining years of their deals.
Stafford, the No. 1 pick in the 2009 NFL draft, signed a six-year contract worth up to $78 million with $41.7 million in guarantees. Vanden Bosch signed a $26 million, four-year deal last year.