Level 61

Total Experience Required 1,254,826 [confirmed]

Level 100 progress: 18.38%

This is roughly:
Killing 4,183 people in Warzone, or...
Killing 4,269 people in Execution, or...
Killing 3,545 people in Wingman, or...
Scoring 896,305 points in Guardian, or...
Scoring 2,727,883 points in Annex, or...
Scoring 1,651,087 points in Submission.

Horde (TU4)

Completing 6,275 waves on Casual, or...
Completing 4,183 waves on Normal, or...
Completing 3,138 waves on Hardcore, or...
Completing 2,510 waves on Insane.

Or a combination of the above. Have fun!