Harmonix has fully confirmed that Rock Band 4 will be backwards compatible on your old instruments and songs.
Harmonix confirmed this via the E3 2015 YouTube livestream. It was speculated before Rock Band 4 would be backwards compatible, but now it’s great to see it being fully confirmed.
Backwards Compatibility on Rock Band 4 will allow be for the same console family. PS3 instruments will work on PS4 and Xbox 360 instruments will work for Xbox One.
This will save you money buying the $250 Rock Band 4 bundle. It will allow lots of gamers to dig up their old instruments from the basement.
Harmonix also fully confirmed that Rock Band 4 will also allow you to sing all of your old DLC songs. Again, this is a great feature as it will save people a lot of money.
Rock Band 4 will be released for the Xbox One and PS4 from October 6th, 2015.