Level 31

Total Experience Required 144,013 [confirmed]

Level 100 progress: 2.11%

This is roughly:
Killing 481 people in Warzone, or...
Killing 490 people in Execution, or...
Killing 407 people in Wingman, or...
Scoring 102,867 points in Guardian, or...
Scoring 313,072 points in Annex, or...
Scoring 189,491 points in Submission.

Horde (TU4)

Completing 721 waves on Casual, or...
Completing 481 waves on Normal, or...
Completing 361 waves on Hardcore, or...
Completing 289 waves on Insane.

Or a combination of the above. Have fun!