Technically, it's 8 years. Also, that's based on
#Spurs wanting/being able to match what a team offers. After 4 years (3 years from now), the Spurs can offer a contract (qualifying offer). Making him an RFA. Harper can still negotiate with other teams, and the Spurs have a right to match. However, there will be team(s) that will make a stupid and insane offers. The Spurs will not be able to match with Wemby and Castle Super Max contracts.
CJ McCollum made it clear that as player president, he does NOT want teams to retain their draft picks via aprons. Hints why it was put in current CBA. He was so salty he couldn't beat GSW. He literally built a law to make sure homegrown has to go.
Unless NBA CBA corrects CJ saltiness. It is what it is.