Well this is no surprise as indie games are more and more prominent in the games industry as of last year.
Unreal was the first to announce at GDC 2015 that they were removing the subscription fee from Unreal and letting everyone use it with a royalty charge of 5% after the first $3’000 per quarter. This is close to the deal they had with Unreal Engine 3 except that was a royalty only after $50’000 in revenue.
Unity is taking a different route and just not having any royalty at all with their free version of Unity 5 which is pretty fair if you ask me, the things you will get for subscribing is priority bug support, team licencing, etc. But if you reach over $100’000 in revenue/funding then you have to upgrade to their Professional Edition.
Source 2 is completely free as well just like Unity and Unreal, but there are rumors that if you don’t want royalty charges then you have to release it on Steam. Which is still getting royalty from Valve but I don’t how this works.