Steam Workshop integration is part of the base game; no DLC required. Since v3.0.0, workshop items are compatible across all DLC combinations, so AMPLIFIED resource packs can be loaded by non-AMPLIFIED clients and vice versa.

Workshop mods are mostly limited to resource modifications: graphics, sounds, music, plus a few basic stats for enemies and items. Support for Lua mods (which can alter gameplay much more significantly) was introduced in the Synchrony DLC, along with a mod portal for exploring and downloading mods in-game.