Level 58

Total Experience Required 1,048,332 [confirmed]

Level 100 progress: 15.36%

This is roughly:
Killing 3,495 people in Warzone, or...
Killing 3,566 people in Execution, or...
Killing 2,962 people in Wingman, or...
Scoring 748,809 points in Guardian, or...
Scoring 2,278,983 points in Annex, or...
Scoring 1,379,385 points in Submission.

Horde (TU4)

Completing 5,242 waves on Casual, or...
Completing 3,495 waves on Normal, or...
Completing 2,621 waves on Hardcore, or...
Completing 2,097 waves on Insane.

Or a combination of the above. Have fun!