Was just skimming through the fine print at TDA. I came across this section about automatic fills for option expiration. It may not be automatic...
I am responsible for instructing you as to my intention to exercise
options contracts before the expiration date. Absent proper and timely
exercise instructions from me, you have no obligation to exercise any
right, privilege or obligation of any option for my Account. I agree that
my failure to provide you with proper and timely instructions may result in
the option expiring worthless, even though it may have a monetary value
on the expiration date. I agree to read carefully the Margin Handbook for
additional terms and important information regarding options exercise.
I am responsible for instructing you as to my intention to exercise
options contracts before the expiration date. Absent proper and timely
exercise instructions from me, you have no obligation to exercise any
right, privilege or obligation of any option for my Account. I agree that
my failure to provide you with proper and timely instructions may result in
the option expiring worthless, even though it may have a monetary value
on the expiration date. I agree to read carefully the Margin Handbook for
additional terms and important information regarding options exercise.