If you're striving to become a true Pokemon Master in Pokemon Go, you'll need to reach Level 40, the highest obtainable level in the game. Pokemon Go doesn't make reaching Level 40 easy, as the game requires exponentially more XP to level up as players progress farther into the game. In order to get to Level 40, players will need to collect a total of 20 million XP, with 5 million XP needed just to level up from Level 39 to Level 40.
So what do you get for reaching Level 40? Surprisingly, not very much. Players receive 40 Ultra Balls, 40 Max Potions, 40 Max Revives, 40 Razz Berries, 4 Egg Incubators, 4 Lucky Eggs, 4 Lure Modules, and 4 Incense. Reaching Level 40 won't unlock Master Balls, Honey, or any of the other items still hidden in Pokemon Go's game data. Nor does the game unlock any Legendary Pokemon or Ditto, who players still haven't figured out how to unlock.
So far, only one player has reportedly reached Level 40 and they did it with the help of an automated bot in order to test the game's capabilities. According to that player, they used 131 Lucky Eggs to reach Level 40 and averaged about 280,000 XP per hour.
The fact that Niantic included Lucky Eggs indicates that they plan to increase the Level Cap at some point, so maybe Level 40 is just another step in the Pokemon Go journey instead of the destination.