Level 72

Total Experience Required 2,277,409 [confirmed]

Level 100 progress: 33.36%

This is roughly:
Killing 7,592 people in Warzone, or...
Killing 7,747 people in Execution, or...
Killing 6,434 people in Wingman, or...
Scoring 1,626,721 points in Guardian, or...
Scoring 4,950,890 points in Annex, or...
Scoring 2,996,591 points in Submission.

Horde (TU4)

Completing 11,388 waves on Casual, or...
Completing 7,592 waves on Normal, or...
Completing 5,694 waves on Hardcore, or...
Completing 4,555 waves on Insane.

Or a combination of the above. Have fun!