The three G.O.R.E weapons each have three tiers and can be upgraded, although the process is greatly enhanced by players who find G.O.R.E. enhancements. Not coincidentally, these can be found on the three new bosses added with the patch. The full patch notes also include a few art fixes and minor quality-of-life improvements, the sort of things that go very nicely with your new anniversary guns.
[Update: The team has updated the patch notes to clarify that not all of the new weapon components can be purchased through the cash shop. Specifically, "all components that are required to build the weapons are earned in-game using resource harvesters, killing boss mobs, and from high-level merchants (for in-game currency only)." Players may purchase optional G.O.R.E. enhancements and new boss baits through the cash shop, although both of these drop from monsters as well.]