Although a lot of information has been released on the multiplayer portion of the game, David Vonderhaar (multiplayer design director) was kind enough to reveal more on how the game's multiplayer level progression system works.

The game will have 55 levels with 10 Prestige levels - leveling up will be much faster thanks to all the new medals, challenges and other XP boosts. You won't be able to unlock everything in the game by just by reaching level 55; you will need to Prestige multiple times to access everything.

You will gain 1 unlock token every time you level up and they can be used to unlock new weapons, Perks, Scorestreaks and equipment in Create a Class. For example, at level 10 you will have 10 unlock tokens available. Create a Class is unlocked at level 4 and when it's unlocked, you will be given a few free items:

1x Assault Rifle
1x Sub Machine Gun
1x Light Machine Gun
1x Shotgun
1x Sniper Rifle
3x Perks, one from each perk category
1x Lethal Grenade
1x Tactical Grenade or Equipment
At level 5 you will receive one new Perk and at level 6 one equipment. Scorestreaks are unlocked at level 7 and you can choose 3 for free - optionally you can spend your unlock tokens to get 3 more. Level 8 gives you another perk and level 9 a new Scorestreak.

After reaching level 10 the system settles into a simpler pattern that repeats through all 55 levels and Prestige levels. Every major rank change, which is every 3 levels, you will be given a weapon and a bonus. Here's the general idea of the level progression system:

Level 4 - Create a Class unlocked + free items
Level 5 - 1x Perk
Level 6 - 1x Equipment
Level 7 - Scorestreaks unlocked + 3 given for free
Level 8 - 1x Perk
Level 9 - 1x Scorestreak
(pattern starts)
Level 10 - Weapon + 1x bonus (major rank)
Level 11 - Equipment
Level 12 - Scorestreak
Level 13 - Weapon + 1x bonus (major rank)
Level 14 - Equipment
Level 15 - Scorestreak
Level 16 - Weapon + 1x bonus (major rank)
and so on ...
Vonderhaar also stated that the system is currently in the final stages, but changes are possible before the game ships to stores.