I think whether he is a fifth year option depends on the fifth year option formula and how much of an increase in annual pay it would be. RBs are not well paid and the number may not be that much under the formula.
I thought it was likely no fifth year option, but if he continues to build on his best year, there is some chance. Seems like Chiefs players and coaches like him and say he can play.
If 5th year option number is too high, I would guess he gets tendered on some level and could be a re-sign depending on offers from other teams.
For players selected between 11th and 32nd in the draft, the same calculation is used to compute their salaries. The difference lies in what is averaged; rather than the top ten, the 3rd-25th highest Prior Year Salaries for the player’s position will be used.