It can decrease or leave open interest unchanged, depending on whether the buyer is also opening or closing a position.
This order is used to a new long position. When you execute a BTO order: buy to open sell to close
You relinquish your rights and realize a profit or loss based on the difference between your initial BTO premium and the current STC premium. It can decrease or leave open interest unchanged,
This order is used to a position you previously opened via BTO. When you execute an STC order: Action: You sell your existing contract to another party. buy to open sell to close