this is probably a very stupid question.. but I have to ask... if an option contract has say 900 volume today... but 0 open interest,,, is that because open interest does not update intraday??
Open interest is the amount of trades already placed and held by traders. Volume is the number of contracts that got traded that very day. If it was zero open interest, there were no trades on that option until today where 900 contracts were bought on that contract.
Open Interest is determined by the clearing house/trade settlement process. Reporting is usually delayed by a day, so many so-called Trade Reports that show volume and open Interest show today's volume and yesterday's open interest. Many data vendors mis-assign the volume to the wrong day. Some exchanges report same-day open interest, but usually several hours after the close.
Open interest updates at night from the OCC. We have the data a few hours in the morning that we publish. Here's a graph of OI by option: