You might see versions 2.0, or even 3.0 floating around. However, (often written as v3.15 or Mod 315) is considered the "Goldilocks" update. It offers:

Version 3.1.5 is particularly significant within the mod's history. In the lifecycle of software development, later versions do not always equate to better performance; sometimes, "feature creep" can bloat a project. However, version 3.1.5 is widely regarded by the community as the "Goldilocks" release. It introduced a massive array of playable units—including specialized SWAT teams, hazmat units, and distinct fire apparatus—while maintaining a level of stability that later, more experimental versions sometimes struggled to achieve. For players looking to run a smooth freeplay mode, managing traffic accidents, structure fires, and criminal pursuits without frequent crashes, 3.1.5 remains the standard-bearer.

You have the download link. Now, how do you install it without destroying your game? Follow this precisely.