Level 54

Total Experience Required 816,062 [confirmed]

Level 100 progress: 11.96%

This is roughly:
Killing 2,721 people in Warzone, or...
Killing 2,776 people in Execution, or...
Killing 2,306 people in Wingman, or...
Scoring 582,902 points in Guardian, or...
Scoring 1,774,048 points in Annex, or...
Scoring 1,073,766 points in Submission.

Horde (TU4)

Completing 4,081 waves on Casual, or...
Completing 2,721 waves on Normal, or...
Completing 2,041 waves on Hardcore, or...
Completing 1,633 waves on Insane.

Or a combination of the above. Have fun!