Level 64

Total Experience Required 1,491,521 [confirmed]

Level 100 progress: 21.85%

This is roughly:
Killing 4,972 people in Warzone, or...
Killing 5,074 people in Execution, or...
Killing 4,214 people in Wingman, or...
Scoring 1,065,373 points in Guardian, or...
Scoring 3,242,437 points in Annex, or...
Scoring 1,962,528 points in Submission.

Horde (TU4)

Completing 7,458 waves on Casual, or...
Completing 4,972 waves on Normal, or...
Completing 3,729 waves on Hardcore, or...
Completing 2,984 waves on Insane.

Or a combination of the above. Have fun!