Speed runners are an interesting breed of gamers, playing games over and over again to find every possible way to take down games as quickly as possible. Interestingly enough, while Breath of the Wild might be the biggest, most epic entry in the Zelda franchise, its unique design makes it surprisingly well suited for speed-runs. Minor spoilers follow for those who have yet to pick up the game.
The opening of the game forces players through a series of simple objectives before giving them complete and utter freedom to tackle the rest of the game as they see fit. Most gamers will instinctively set out to explore the world, become stronger, and acquire better gear, but those looking for a challenge are free to tackle the endgame right away. This of course requires considerable skill and know how on the part of the gamer, but those looking to set record times need to know how shave off every fraction of a second in the process. For example, seconds can be saved by using the Smash Bros. Link Amiibo to summon a horse right away (a technique considered controversial by some in the community), or by playing the game in German.
Several speed runners have already managed to bring their completion time down to under an hour; the first to do so was a player who goes by gymnast86. However, the current record holder is Venick409 who has posted a time of 54:05 with the run you can watch below.
Considering the fact the game has only been out for less than two weeks, these accomplishments are quite impressive and one can only imagine that with time, runners will find every trick possible to bring that number down.