Earlier today, Epic accidentally made available a new game mode that was supposed to be tested in early 2018. The limited time event was meant to test the new shooting model mechanics, including recoil and crosshair sights.
The event was live for over an hour, and was promptly turned off as soon as possible after the developers noticed the mistake. In a following Twitter announcement, they explained it as "a slip up" and promised to look into it.
The new shooting model is an upcoming proposed change to one of Fortnite's core mechanics, and is meant to alter the way guns behave. This is what the official dev post outlined back in November:
"We've been internally playtesting an overhaul of our shooting model to remove random bullet spread while aiming down sights. We want to improve shooting while maintaining the usefulness of building cover while under fire and without changing engagement distances or the flow of the game."
So far, the theory of those changes has polarised the community, though Twitter responses to this recent event seem to indicate quite a few players enjoyed the alterations. The actual, real shooting model test will take place in January 2018, and will be a new limited time game mode instead of a Beta so console players can take part.