Shai Gilgeous-Alexander is on a rookie contract and signed an extension that is to begin the following season. Therefore, he has what is known as a "poison pill" contract. He can no longer be traded for a player making equal money. Instead, his current salary is averaged along with the salaries he is to receive in his extension, and that average becomes his incoming salary for trade purposes. His outgoing value for the Thunder will be $5.4M while his incoming value for the receiving team will be $29.6M.
Shai Gilgeous-Alexander currently has a team option for the Thunder this season. The Thunder may decide to decline their option which would make him an unrestricted free agent. You may accept or decline this option, by default it will be accepted. You may also update his contract to perform actions such as a Sign & Trade.