Level 50

Total Experience Required 625,387 [confirmed]

Level 100 progress: 9.16%

This is roughly:
Killing 2,085 people in Warzone, or...
Killing 2,128 people in Execution, or...
Killing 1,767 people in Wingman, or...
Scoring 446,705 points in Guardian, or...
Scoring 1,359,537 points in Annex, or...
Scoring 822,878 points in Submission.

Horde (TU4)

Completing 3,127 waves on Casual, or...
Completing 2,085 waves on Normal, or...
Completing 1,564 waves on Hardcore, or...
Completing 1,251 waves on Insane.

Or a combination of the above. Have fun!