Level 48

Total Experience Required 544,866 [confirmed]

Level 100 progress: 7.98%

This is roughly:
Killing 1,817 people in Warzone, or...
Killing 1,854 people in Execution, or...
Killing 1,540 people in Wingman, or...
Scoring 389,190 points in Guardian, or...
Scoring 1,184,492 points in Annex, or...
Scoring 716,929 points in Submission.

Horde (TU4)

Completing 2,725 waves on Casual, or...
Completing 1,817 waves on Normal, or...
Completing 1,363 waves on Hardcore, or...
Completing 1,090 waves on Insane.

Or a combination of the above. Have fun!