Subscribe to download
XCom Legion

Presently the mod will only increase the default squad size from 4 to 6. So with the possible upgrades during the game you can reach a squad size of 8 people.

I highly recommend using this mod as well so you can control the 7th and 8th slot in the squad menu.
http://steamcommunity.com/sharedfiles/filedetails/?id=619112580

IMPORTANT NOTES:

1. This mod does increase the number of people who come with you. However, you can only reliably select the first six squad members. If you've unlock squad member 7 and 8, after setting your initial 6, you can select Auto-fill to add the others and they join you at the drop zone.

2. If you play in Hardcore (like I do), any mod that you activate, must remain in place in order to not ruin or invalidate your save. So if you're playing in Hardcore, be certain you want this before you use it. No idea if it has a similar impact on non-Hardcore games.

Details on what's done are below:
This mod makes a change to the XCom2 Configuration files.

It does NOT modify the default .ini files located in the main game directory. It instead updates the .ini files that are generated and stored in your User directory (i.e. ...\Documents\my games\XCOM2\XComGame\Config). These files trump the default .ini configuration files and are what should be modded.

The configuration files that are updated are:
XComGameData.ini

UNINSTALLING

1. Unsubscribe to the mod.
2. Ensure that it's not located in your mod list at start-up.
3. If you it still seems like it's in effect, then go to the Config folder in your XCom 2 User folder. It'd be something like: ...\Documents\my games\XCOM2\XComGame\Config
4. Delete the XComGameData.ini
5. Restart XCom 2 and it should regenerate a new XComGameData.ini file