The Epic First Run programme allows developers of any size to claim 100% of revenue if they agree to make their game exclusive on the Epic Games Store for six months.
After the six months are up, the game will revert to the standard Epic Games Store revenue split of 88% for the developer and 12% for Epic Games.
That was my understanding. I don’t know how Fortnite is doing, but I thought perhaps they are running out of money when they announced this new “thing”.