Level 45

Total Experience Required 440,381 [confirmed]

Level 100 progress: 6.45%

This is roughly:
Killing 1,468 people in Warzone, or...
Killing 1,498 people in Execution, or...
Killing 1,245 people in Wingman, or...
Scoring 314,558 points in Guardian, or...
Scoring 957,350 points in Annex, or...
Scoring 579,449 points in Submission.

Horde (TU4)

Completing 2,202 waves on Casual, or...
Completing 1,468 waves on Normal, or...
Completing 1,101 waves on Hardcore, or...
Completing 881 waves on Insane.

Or a combination of the above. Have fun!