Hello. Right now, UNITTYPE_Custom1 is used by Legion. The UNITTYPE_Custom2 tag is currently most actively used by Union. UNITTYPE_Custom3 and UNITTYPE_Custom4 are currently not being actively used, to my knowledge. This may change in the near future. Between myself, CyberpunkPanda, billthebluebot, and Anonemous2, there are currently enough planned projects that UNITTYPE_Custom3 and UNITTYPE_Custom4 may be used soon. There are at least three concepts that may be worked on soon between the four of us that require usage of new UNITTYPE_Custom tags: 1. Surveyor Protocol - CyberpunkPanda and I have been considering working on a "support faction" that adds a new tech path + a few units to MLA, Legion, and Union alike. I.e. this group of units would be available to all 3 factions. 2. The "Bugs" - billthebluebot and Anonemous2 are planning to begin working on an "AI-only faction" that can allow players to experience a new Co-op vs AI experience. 3. The "Berserkers" - I have been planning to begin working on a separate "AI-only faction" as a proof of concept. This concept will probably only reuse MLA models, but there is significant UI work that must be done that can be reused for the "Bugs" concept by billthebluebot and Anonemous2. Ideally, all 3 of these concepts would be compatible together in the future, alongside Legion and Union. It is possible to fiddle around with the existing tags such that this can be done (Bugs and Berserkers can share UNITTYPE_Custom4, with enough coordination, for example), but things would be easier with additional UNITTYPE_Custom tags. Furthermore, we don't wish to hog all of the UNITTYPE_Custom tags. There's no real rush on this request, but we are hoping that more UNITTYPE_Custom tags will be added eventually. Additionally: If new UNITTYPE_Custom tags are added, existing mods such as Legion and Queller won't immediately be broken by this addition. However, they might be broken by the first mods to take advantage of these new tags. As a result, the longer the gap between the addition of these tags and the first mods to actually use them, the longer the maintainers and developers of Legion, Queller, and other mods will have to prepare necessary changes.