"Throughout his first three seasons in the NFL, Quinton has shown consistent development and has become a key contributor in our defense," said 49ers general manager Trent Baalke. "We have certainly seen his positive impact on the field and in our locker room, but we also recognize the impressive work he does in the community year round. We are pleased to extend the contract of young players like Quinton and are excited to see him continue his career with the 49ers."