If you buy a digital copy of Destiny for last gen consoles you will get a free copy for current gen

Today it was announced that last gen console owners who buy Destiny will be able to upgrade their game to the PS4, or Xbox one if they decide to upgrade their console.

However if you want to upgrade you will have to do it before January 2015 as that is when the deal expires. Destiny is released on September 9th 2014 and is available on PS4, PS3 Xbox 360, Xbox one and PC.