Originally Posted by xliioper

The big 3 domestic carriers did lengthen stopover limits for US48 fares during Covid, but they've since all retreated back to 4 hours. WN is an exception and has extended the limit beyond 4 hours in recent years. First to 6 hours, and more recently up to 8 hours (as shown below). If you use advance controls on ITA Matrix to specify a carrier, it will typically show many more valid fares on a routing than the airline fare search sites will show which are typically only the shorter connection options. These may be single through fares, or broken fare options. Basically, any US48 itin with a layover over 4 hours will involve broken fares due to the no stopovers provision in the fare rules. You can also use Google Flights multi-city to contruct itins with layovers over 4 hours with broken fares. If layover is under 4 hours, Google Flights multi-city search will often combine them on a single fare component as that is typically cheaper than broken fares where you are paying separate fares on each segment.