Fallout 76 has been updated to version 1.58 today by Bethesda Softworks. You can find out the complete patch notes for this update from here.
This update brings in support for a brand new Halloween event for Fallout 76. The download size is a little over 2 GB on PC, and around 9 GB on PS4, PS5, and Xbox consoles. You can get the patch notes on reddit, or you can just have a look at them below.