The Celtics now have five potential core pieces — White, Jayson Tatum, Jaylen Brown, Robert Williams, and Marcus Smart — under contract through at least the 2023-24 season. Smart and Williams are locked up through 2025-26 and Tatum has a player option that year. Part of the reason Stevens jumped at the chance to add White was the three years remaining on his deal after this season. “This is good for three months,” said Stevens. “But this is really good for three and a half years.”