There are 7 different level tiers:

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 coin bet:

Roulette: 100xp

Cases & case battles: 70xp

Coinflip: 10xp

Matchbet single or Bet Builder bet: 25xp (any odds)

Matchbet combo bet: 50xp (any odds)

Matchbetting XP is credited once a bet has fully settled. For combo bets, all selections in your bet need to be settled before XP is credited.

You can see how much XP is required, and how many keys you'll receive for each level here.