What is the difference between American and European exercise style options?

n American-Style option seller (writer) may be assigned an exercise at any time until the option expires. This means that the option writer is subject to being assigned at any time after he or she has written the option until the option expires or until the option contract writer closes out his or her position by buying it back to close. Early exercise happens when the owner of a call or put invokes his or her rights before expiration. As the option seller, you have no control over assignment, and it is impossible to know exactly when this could happen. Generally, assignment risk becomes greater closer to expiration, however even with that being said, assignment can still happen at any time when trading American-Style Options…

…

In the case of U.S. exchange listed options cleared by OCC, IBKR's deadline for providing notification of intent to exercise is 17:25 ET if the option is being exercised prior to expiration. At expiration, notice of intent to exercise is generally not required as OCC will automatically exercise options that are in-the-money by $0.01 or more…

If a long option is not in-the-money by at least $0.01 at expiration it will not be automatically exercised by OCC. If it is in-the-money by at least that amount and you do not wish to have it exercised, you would need to provide IBKR with contrary instructions to let the option lapse. These instructions would need to be entered through the TWS Option Exercise window prior to the deadline as …