SimCity 4 modders are making previously-unheard-of DLL plugins and mods due to recent advances, enabling changes of tweaks to how it runs that prior modders would have considered impossible. Over the past few months these types of deep, game-altering mods, previously restricted to just a couple famous examples, have proliferated into dozens of tweaks to quality of life and brand new game features.

These new mods are so revolutionary because they access SimCity 4’s DLL files, the library of binary files containing shared resources used across the entirety of SimCity 4. The biggest immediate impact is a mod enabling more building styles. That’s huge: SimCity 4 players have had four tilesets of buildings for 20 years. Now they can have a lot more. There are also a host of mundane fixes marching out. Stuff like improving game stability, enabling new resolutions, adding autosaves, or more directly access information from under the game’s hood about demand for building types.

The 21-year-old SimCity 4 Deluxe is considered by many to be the peak of city building games for simulating a rich, deep model of how cities operate. That preference for this specific game after all this time, and all the city builders that have come after, has fueled a rich modding and graphics development scene around the game for the past two decades. Modders were always hampered, however, because they didn’t have access to the deeper reaches of how it worked: Just the fairly surface-level stuff.

The major announcement by a moderator on the longstanding Simtropolis forums brought attention to the new wave of mods, in part because the good news came with a caveat: The new wave of DLL mods would not work well if at all on older Windows disc versions, or macOS ports, of SimCity 4—just the current version available digitally.

The story’s pretty straightforward: The first major DLL tweak was a cheeky little cheat file, SC4 Extra Cheats DLL, that Maxis developers had authorized the release of. The second was SC4Fix, a release by modder simmaster07 that solved two huge bugs in a modded SC4 game—but that mod was very specific and limited in scope. Since then, though, other modders have piled in on that work to expand on it and figure out how other things inside SC4 work, bringing the community to this watershed moment in modding.

“Thanks to the efforts of those continuing simmaster07’s line of work, namely Null 45 and memo, these sorts of revolutions are about to become more commonplace, bringing with them everything from improved game stability on modern systems, to long-requested new features and quality-of-life (QoL) improvements.  Null 45 has already released over a dozen DLL mods on the STEX since November, one of the most recent of which allows more Building Styles.  While I can’t reveal too much at this point in time, I will note that DLL files will become important components of major SC4 mods in the very near future.  Suffice to say, we’re entering a very exciting time in the SC4 modding community,” said moderator Tarkus on Simtropolis.

Those interested in the SimCity 4 modding community can buy a copy of SimCity 4 Deluxe version 1.1.641 that’s compatible with the mods via several modern sites, with most SimCity modders recommending the version purchased from GOG.