Getting to the current level cap of 40 in Pokémon GO takes 20 million XP. That's 200,000 Caterpie caught, or 40,000 evolutions, without Lucky Eggs. Even with Lucky Eggs, those numbers cut in half are still a major pain. The final level-up between 39 and 40 takes 5 million of those XP points. Playing legitimately, most estimates say that such a feat could take about a year. The game has been out for less than a month, and somebody on Reddit has managed to hit that level cap. Naturally, they admitted almost straightaway that they used a leveling bot that played the game for them via GPS spoofing and other hat tricks, along with a huge stack of Lucky Eggs.
Redditor _problemz, playing under the alias ra1ndr0pz, used a bot to generate an average of 280,000 XP per hour, with the bot playing the game in much the same way a human would, but much faster and more perfectly - albeit with the aid of 131 Lucky Eggs. Because of this, _problemz said that they refuse to participate in gym battles, for the sake of keeping them fair for others. They did, of course, hit up the gyms a few times while playing legitimately, before the bot kicked in. The bot user also said that, with the experiment concluded, they had written to Niantic to have their account deleted, rather than selling the high-level account or using it to run services for other players once future updates with trading roll out.
The rewards for level 40 are pretty sweet, but not quite enough on their own to motivate somebody to undertake the monumental feat. Players hitting level 40 get 40 Hyper Balls, 40 Max Potions, 4o Max Revives, 40 Razz Berries, 4 Incense, 4 Lure Modules, 4 Incubators, and, curiously, 4 Lucky Eggs, possibly pointing to a future increase in the game's level cap. At that high a level, the botter's top Pokemon sported 3,375 CP, making it incredibly potent in battle, if it were to be used. Since players around level 30 tend to encounter wild Pokémon with upwards of 1,000 CP, it's not entirely ludicrous to think that a strong, fully leveled and fully evolved Pokémon for a level 40 player could reach such heights. Since the bot focused on garnering Trainer XP, however, even stronger Pokémon are certainly possible, with some serious work.