This game has Endurance Racing DLC now. LMP1 (Endurance A) and LMP2 (Endurance B) multi-class racing on 90min-6 hour races (depending on your preference). The update is ridiculously massive - a LOT of changes, new endurance features (pit stops, drive times, driver per car, fatigue, etc). The update itself is free, but the new prototypes cost £6. I highly recommend it.
Now they need to find a way to mash the GT and LMP DLC into one on track mode for those who own both.