Level 24

Total Experience Required 75,167 [confirmed]

Level 100 progress: 1.1%

This is roughly:
Killing 251 people in Warzone, or...
Killing 256 people in Execution, or...
Killing 213 people in Wingman, or...
Scoring 53,691 points in Guardian, or...
Scoring 163,407 points in Annex, or...
Scoring 98,904 points in Submission.

Horde (TU4)

Completing 376 waves on Casual, or...
Completing 251 waves on Normal, or...
Completing 188 waves on Hardcore, or...
Completing 151 waves on Insane.

Or a combination of the above. Have fun!