During the stream this morning, Infinity Ward revealed a few of the 10 total Classic Weapons that will be in Call of Duty: Infinite Warfare.
As noted before, Classic Weapons are fan favorite weapons from previous Call of Duty games. In Infinite Warfare, the Classic Weapons can be unlocked via prestiging. Each time you prestige, you get a classic weapon unlock token, which you can use to select which weapon you want to unlock.
In the stream, Infinity Ward revealed five of the weapons: Intervention (returning as TK141, UMP (returning as MacTav 45), SPAS 12 (returning as the S-Ravage), the M1, and the ARX-160 from Call of Duty: Ghosts.
These five weapons will be visible in the beta, but you cannot use them.
Thanks @VegasPenguin and @TrollinThunder for the tips!