Level 88

Total Experience Required 4,573,128

Level 100 progress: 67%

This is roughly the same as:

Killing 7,622 people in Warzone, or...
Killing 7,778 people in Execution, or...
Killing 6,460 people in Wingman, or...
Scoring 1,633,260 points in Guardian, or...
Scoring 4,970,792 points in Annex, or...
Scoring 3,008,637 points in Submission.

Horde (TU4)

Completing 11,433 waves on Casual, or...
Completing 7,622 waves on Normal, or...
Completing 5,717 waves on Hardcore, or...
Completing 4,574 waves on Insane.

Or a combination of the above. Have fun!