There are 7 different tiers:
Rust (1 hour cooldown)
Bronze (2 hour cooldown)
Silver (3 hour cooldown)
Gold (6 hour cooldown)
Diamond (6 hour cooldown)
Uranium (6 hour cooldown)
Unbreakable (6 hour cooldown)
All of these tiers correspond to a key, meaning any keys granted for a level under the Rust tier will result in a Rust key being given out.
Each game mode gives a different amount of XP, and your total XP decides your level. Here's a list of how much XP each game mode gives you for every 1 Empire Coin bet:
Roulette: 100xp
Cases & case battles: 90xp
Coinflip: 10xp
Match bet single or Bet Builder bet: 25xp (any odds)
Match bet combo bet or system bet: 50xp (any odds)
Match bet ‘free money’, ‘no risk’ and ‘bet refund’ bets: 0xp
Match bet bets where odds are set to 1.00 due to refund or cancellation: 0xp
Match betting XP is credited once a bet has been fully settled. For combo, system and bet builder bets, all selections in your bet need to be settled before XP is credited. If a combo turns into a single after one or more bets have been cancelled or voided, then it will only give 25XP per Empire Coin wagered. The same XP rates apply to cashed out wagers.
You can see how much XP is required, and how many keys you'll receive for each level by clicking on the information icon next to "Bonus Cases":
