The OCC put out this memo in case of an 'unscheduled market closing" https://www.theocc.com/components/docs/about/publications/unscheduled-market-closings-guide.pdf
Thanks for posting this! It is definitely not what I expected when it comes to SPX which I trade. It looks like in most cases they'll turn PM options into AM SOQ options for the next day after a halt that goes across expiration, which is crazy. I had deduced from everything I could find up to now that they'd use the last traded price of the SPX, which oddly it looks like they are doing for some other products but not SPX. This makes an EOD trading halt a real show stopper for me!