Level 4

Total Experience Required 3,310 [confirmed]

Level 100 progress: 0.05%

This is roughly:
Killing 12 people in Warzone, or...
Killing 12 people in Execution, or...
Killing 10 people in Wingman, or...
Scoring 2,365 points in Guardian, or...
Scoring 7,196 points in Annex, or...
Scoring 4,356 points in Submission.

Horde (TU4)

Completing 17 waves on Casual, or...
Completing 12 waves on Normal, or...
Completing 9 waves on Hardcore, or...
Completing 7 waves on Insane.

Or a combination of the above. Have fun!