The intersection of Skyrim Special Edition (SSE) version 1.5.97 and the Unofficial Skyrim Special Edition Patch (USSEP) is a cornerstone of the "legacy" modding community. While the game has since moved to version 1.6+ (Anniversary Edition), many players deliberately maintain 1.5.97 for its superior stability and compatibility with specific SKSE plugins.  The Core Version: USSEP 4.2.5b 

If you are building a modlist today, you might wonder: Is 1.5.97 still the gold standard? Here is everything you need to know about maintaining a stable 1.5.97 setup and finding the elusive Unofficial Skyrim Special Edition Patch (USSEP) to match it. Why Version 1.5.97?

require the NetScriptFramework, which only functions on version 1.5.97. downgrade your game to 1.5.97 while keeping USSEP compatibility?

If you want the benefits of the latest USSEP updates while keeping your 1.5.97 executable for mod compatibility, use the Skyrim Special Edition Downgrade Patcher The Method:

Current Status: This version is technically "retired" and hidden on the Unofficial Skyrim Special Edition Patch Nexus page because the authors only officially support the most recent game version.