Yes, for domestic flights Executive Platinum flyers (basically 100K miles or more each year) get upgraded to any open first class seats for free. At other level

Yes, for domestic flights Executive Platinum flyers (basically 100K miles or more each year) get upgraded to any open first class seats for free. At other levels (50K+ or 25K+) can also upgrade to available empty first class seats, but it can cost a small amount.