Golden State sells relatively low on JK, but brings in 28 year old Hunter, who fits in perfectly in the second unit or can start when Butler is out. GS is also thin on draft capital, so they send seldom-played Santos to Detroit for a future SRP, to make the math work.
Cleveland is in financial purgatory, and this trade doesn't help. But Kuminga is 5 years younger than Hunter. And more athletic, giving them a slasher that they don't have. A move like this is about as risky as they can get with being in the second apron. But it could help infuse new energy to get them back to the top of the East.
Detroit helps facilitate by gaining depth in Santos on his expiring contract for a SRP.