Treyarch’s David Vondehaar has explained the unlocking and levelling system of Black Ops 2‘s multiplayer in a community forum post on the official boards.
There will be 55 ranks, earning one unlock token with each level, and the ‘create-a-class’ option made available at level four, along with a dozen free bits of equipment for you so you don’t have to blow the four unlock tokens you’ve earned if you don’t want to.
More equipment, perks and scorestreaks are slotted in from levels five through ten, whereupon it starts to settle into a pattern. Vondehaar describes the pattern as follows: “At every major rank change, which is every 3 levels, we give you a gun and usually “something else” as a bonus for reaching a major rank change. In general, it goes like this. Level 10 – Weapon + Something Else. Level 11 – Equipment (either lethal or tatical). Level 12 – Scorestreak.”
“This pattern then repeats through all 55 levels with some minor statstical variations or bonuses when they make sense and because the math can’t be perfect.”