Level 44

Total Experience Required 409,418 [confirmed]

Level 100 progress: 6%

This is roughly:
Killing 1,365 people in Warzone, or...
Killing 1,393 people in Execution, or...
Killing 1,157 people in Wingman, or...
Scoring 292,442 points in Guardian, or...
Scoring 890,040 points in Annex, or...
Scoring 538,708 points in Submission.

Horde (TU4)

Completing 2,048 waves on Casual, or...
Completing 1,365 waves on Normal, or...
Completing 1,024 waves on Hardcore, or...
Completing 819 waves on Insane.

Or a combination of the above. Have fun!