Level 71

Total Experience Required 2,165,174 [confirmed]

Level 100 progress: 31.72%

This is roughly:
Killing 7,218 people in Warzone, or...
Killing 7,365 people in Execution, or...
Killing 6,117 people in Wingman, or...
Scoring 1,546,553 points in Guardian, or...
Scoring 4,706,900 points in Annex, or...
Scoring 2,848,914 points in Submission.

Horde (TU4)

Completing 10,826 waves on Casual, or...
Completing 7,218 waves on Normal, or...
Completing 5,413 waves on Hardcore, or...
Completing 4,331 waves on Insane.

Or a combination of the above. Have fun!