Level 56

Total Experience Required 926,536 [confirmed]

Level 100 progress: 13.57%

This is roughly:
Killing 3,089 people in Warzone, or...
Killing 3,152 people in Execution, or...
Killing 2,618 people in Wingman, or...
Scoring 661,812 points in Guardian, or...
Scoring 2,014,209 points in Annex, or...
Scoring 1,219,127 points in Submission.

Horde (TU4)

Completing 4,633 waves on Casual, or...
Completing 3,089 waves on Normal, or...
Completing 2,317 waves on Hardcore, or...
Completing 1,854 waves on Insane.

Or a combination of the above. Have fun!