The level cap for Pokemon GO appears to be Level 40- and a player has managed to hit that cap, and he can tell us what happens when you reach that stage. Luca, who goes by _Problemz on Reddit, has apparently managed to hit Level 40 in Pokemon GO – albeit he did it with the help of a bot – and he informs us that when you hit that level, he received 40 Ultraballs, 40 Max Potions, 40 Max Revives, 40 Razz Berries, 4 Incense, 4 Incubators, and 4 Lure Modules. Amusingly enough, he also got 4 Lucky Eggs, which are items you use to double the XP you get- so chances are that there are plans in place to raise the level cap.
And why did Luca use a bot to hit the level cap, instead of doing it legitimately? Well, that has to do with the game’s insane level curve at higher levels, you see. To reach Level 40 on his own, Luca would need to earn 50,000 XP every day for a full year- which, if you have played Pokemon GO, you know is not just unlikely, it is flat out impossible.
Anyway, the hope here now is that Niantic add more features to the game to make the end game more viable, and actually worth it- adding trading, PvP battles, more Pokemon to collect, and so on, would go a long way towards making sure players stick around and continue to play the game.