Level 30 is the maximum character level in Outriders.
From the story alone you will reach Level 27-28. The remaining level-ups you will get while doing the 55 Side Quests and/or Expeditions. Killing enemies only gives a low amount of XP. Most XP are from story quest completion and various side quest lines. Expeditions give a little amount of XP from the enemies you kill in them.
It’s worth noting there’s also a world level, called “World Tier” and an Endgame Rank called “Challenge Tier” that increases the level of enemies as well as the gear level they drop. Your character level will no longer increase after reaching level 30 but you can keep getting better gear by playing at higher world tiers. There are two Tier Systems – a “World Tier” that affects the Open World, Main Quests, and Side Quests – and a “Challenge Tier” that affects the Expeditions (Endgame Raids). These Tiering Systems are separate from each other, meaning leveling up one won’t give you progress towards the other. You increase the normal “World Tier” by killing enemies in the Open World without dying. You increase “Challenge Tier” by beating Expeditions (Raids) within a set time limit.
World Tier 15 & Challenge Tier 15 are the maximum ranks.
World Tier 15 adds +12 levels to enemies and dropped items (Character Level 30 + 12 Levels = Level 42 cap).
Challenge Tier 15 adds +20 levels to enemies and dropped items (Character Level 30 + 20 Levels = Level 50 cap).
Therefore, the maximum enemy level and maximum gear level is 50. This level cap is only available in Endgame Expeditions.
Each tier levels up the enemies and items. While the level difference between you and the enemies can be difficult at first, it evens out after your gear level has caught up with the enemy level. The game is really designed around gear level rather than your actual character level. The character level is only important to unlock new skills. The maximum gear level you can equip is also dependent on the maximum world tier you have unlocked.
It takes around 10-14 hours for a typical story playthrough and another 10-14 hours for all side quests. This together is enough to reach level 30.
In summary: Level 30 is the maximum Character Level. Level 50 is the maximum Gear Level & Enemy Level. Tier 15 is the maximum Challenge Level.