Level 71

Total Experience Required 2,165,174

Level 100 progress: 31.72%

This is roughly the same as:

Killing 3,609 people in Warzone, or...
Killing 3,683 people in Execution, or...
Killing 3,059 people in Wingman, or...
Scoring 773,277 points in Guardian, or...
Scoring 2,353,450 points in Annex, or...
Scoring 1,424,457 points in Submission.

Horde (TU4)

Completing 5,413 waves on Casual, or...
Completing 3,609 waves on Normal, or...
Completing 2,707 waves on Hardcore, or...
Completing 2,166 waves on Insane.

Or a combination of the above. Have fun!