Not many gamers remember this, but back during the Overwatch beta’s, Blizzard had added the option to increase the server tick rate. This never made it into the game, as Blizzard wanted to gauge how well it worked. Seems it worked out quite nicely as Blizzard is now rolling it out to Overwatch and all of its game modes. That means that both Quick Play and Competitive Play will run with the higher tick rate in place from the start. This also is exactly what many competitive players have been asking for ever since Overwatch was released publically.
Currently, Overwatch does utilize a 60 tick-rate on the servers, yet the client on our PC’s only allow for a 27 tick-rate. Meaning that this ability isn’t available to us until the update rolls around.
While it will take a few weeks for this to be rolled out to all regions, once in place the tick-rate will start at 63 and will dynamically scale according to your bandwidth. Currently, this is only available for the PC, but Blizzard is looking into how they can bring this experience to the console as well.
Source: http://us.battle.net/forums/en/overwatch/topic/20748474858