Earlier this week, Turtle Rock Studios announced that it will no longer be supporting Evolve (now called Evolve Stage 2) in any capacity. In Patch 2.16, also known as their "goodbye patch" Turtle Rock Studios added Halloween Crates, which include a variety of in-game content and skins.
This was accompanied by a FAQ on 2K's website, which stated that "No future updates are currently planned, as development on Evolve Stage 2 is complete."
In Evolve's farewell twitch stream, Media Producer Shane Meyer noted that "since there was a patch to add them, there needs to be a patch to remove them."
So, if 2K is true to their word, no further patches will come for Evolve Stage 2, which means it will be Halloween every day in Evolve, and you can earn Halloween Crates until the end of time.