Transfer from United Airlines to MIAT in Beijing Capital Airport

I'm flying into PEK from the U.S. on United, and transferring to MIAT to continue on to Ulanbataar. I will have to claim and recheck my baggage in PEK. Both airlines appear to use terminal 3. I have a confirmed flight on MIAT but no confirmed seat, since they don't assign seats until check in at PEK. Will I need a Visa since my seat is not yet assigned, and therefore I assume not "confirmed"?