According to documentation on PCGamingWiki and community changelogs, this version introduced:
The file typically refers to a major official update patch for the real-time strategy (RTS) game Supreme Commander , developed by Gas Powered Games. This update, often categorized under the v1.1.3251 to v1.1.3280 build versions, significantly improved game stability and added new content. Key Features of the v1.1 Update
Improved waypoint line rendering and resolved specific crash bugs, such as those occurring when air units refueled on staging platforms.
Included a new mod manager and various lobby changes to streamline multiplayer sessions. File Structure and Usage
Retuned "Air Superiority" across all three factions and adjusted the effectiveness of units like the Aeon Mercy.