Level 43

Total Experience Required 380,207 [confirmed]

Level 100 progress: 5.57%

This is roughly:
Killing 1,268 people in Warzone, or...
Killing 1,294 people in Execution, or...
Killing 1,075 people in Wingman, or...
Scoring 271,577 points in Guardian, or...
Scoring 826,537 points in Annex, or...
Scoring 500,273 points in Submission.

Horde (TU4)

Completing 1,902 waves on Casual, or...
Completing 1,268 waves on Normal, or...
Completing 951 waves on Hardcore, or...
Completing 761 waves on Insane.

Or a combination of the above. Have fun!