Apparently the Celtics exercised the option on Jackson's non-guaranteed season in 2019-2020, which allowed them to stretch the $650k he was owed this year equally over seven seasons, for a cap/tax hit of just over $90k each season.
I'm generally not a fan of utilizing the stretch provision, but I suppose $93k a year won't derail any plans.
The net effect is that Semi can get paid more money this season.