Read confirmed leaks before you post like this. Because the ranking system has already been confirmed.
They are mixing reach with halo 3 ranking system wise. They have brought back aspects of each. They have brought back EXP and credits, however credits are not used for ranking up, but rater solely for purchasing armor, equipment, weapons, and other things for your custom loadout. Credits are also now temporarily called spartan points. (placeholder). Also, with halo 3 and reach, they have merged 1-50 with the symbols. Each number 1=50 gets a reach symbol correspondingly. What happens is, each time you rank up, and you rank up with EXP, you obviously go to the next rank. So lets say you are level 1, recruit. You would rank up to level 2, private. And so on to level 50, inheritor. I hope this cleared things up.