Level 57

Total Experience Required 985,949 [confirmed]

Level 100 progress: 14.44%

This is roughly:
Killing 3,287 people in Warzone, or...
Killing 3,354 people in Execution, or...
Killing 2,786 people in Wingman, or...
Scoring 704,250 points in Guardian, or...
Scoring 2,143,368 points in Annex, or...
Scoring 1,297,302 points in Submission.

Horde (TU4)

Completing 4,930 waves on Casual, or...
Completing 3,287 waves on Normal, or...
Completing 2,465 waves on Hardcore, or...
Completing 1,972 waves on Insane.

Or a combination of the above. Have fun!