Level 98

Total Experience Required 6,429,618

Level 100 progress: 94.2%

This is roughly the same as:

Killing 21,433 people in Warzone, or...
Killing 21,870 people in Execution, or...
Killing 18,163 people in Wingman, or...
Scoring 4,592,585 points in Guardian, or...
Scoring 13,977,431 points in Annex, or...
Scoring 8,460,024 points in Submission.

Horde (TU4)

Completing 32,149 waves on Casual, or...
Completing 21,433 waves on Normal, or...
Completing 16,075 waves on Hardcore, or...
Completing 12,860 waves on Insane.

Or a combination of the above. Have fun!