https://www.gamespot.com/articles/monster-hunter-worlds-new-kulve-taroth-update-how-/1100-6458403/

While the armor and Palico gear side of all this is very simple, weapons are much different. They're handled unlike anything else in the game to date, as you'll receive them as drops at the end of a Siege. The quality depends on your Reward Level, which is dictated by the contributions made by you and your teammates (though you'll receive more from your squadmates). These are referred to as Relics and have randomized stats but otherwise operate as standard weapons, using the models for existing ones.